Tapping the experience and wisdom of friends, family and colleagues, the following tips for travel to the US have been compiled.
Feel free to add comments and I will edit this as I find out more.Thanks to all of you who have helped compile this list

Before travelling:

• try and upgrade the long-haul to business-class. Not only do you get more room, better food, and a skybed, you also get off the plane first, which can be important if you have a connecting flight to catch
• go to a doctor and get some Temazpan (sleeping tablets)
• check the DFAT website for any advice
• Buy electronics, cameras etc in Australia and if under $900 you can claim the Tourist Refund (you get the GST off the price). If the item costs more than $900 see if you can split it in to multiple purchase orders or you won't get anything back. You also have the correct power supply and a local warranty.

While travelling:

• keep hydrated. Sitting in a plane for a long time with only airconditioning can seriously dehydrate you, so keep filling up the water bottle you get on the plane from the water cooler, or ask for a glass of water often - dehydration leads to jetlag.
• avoid drinking too much alcohol. Coupled with dehydration, a hangover on a plane is not pretty.
• Don't assume that anything is provided on US domestic flights. There will usually be a drinks service of some sort, but food is probably optional if it's available at all, and any sort of on-board entertainment is rare. Bring your own.
• You don't have a confirmed seat on a flight in the US unless you're sitting in the gate lounge holding a boarding pass with a seat number on it. Overbooking domestic flights is the norm. Check in early on your way out and you should be alright, assuming no flight cancellations.
• try and get synchronised with your destination time-zone as soon as you can.
• You have two options for locking your baggage on US-originating flights: use TSA-approved locks (with the red diamond marking), or don't lock it. Using real locks pretty much guarantees that either the locks or the bag will be cut open. TSA locks are easily picked; don't pack anything valuable in checked luggage. Some people use numbered cable ties to show if the bag has been opened.
• Customs
  
  • when going through customs, carry a copy of your itinery / e-ticket for your flight home They want proof you'll be leaving
  • Get you or your bags onto the plane. At the stage that they have one, it is far easier for them to find the other and put it on the plane. Airlines generally hate taking bags off planes so the sooner you can get your baggage back into the hold, the less you have to worry.
  • don't joke, be polite, be aware that "Adelaide" can sound a lot like "Italy" if you're not speaking clearly
  • If you see “SSSS” on your US boarding pass (within the US) then you’ll be subjected to secondary security screening where they’ll check you more thoroughly at the security checkpoint – they have no sense of humour and just do EXACTLY what they tell you to do. It’s nothing to be scared of and in fact you may get through security quicker than if you were in the standard line – just be aware
  • When going through security make sure you keep hold of your passport and boarding pass – don’t let them go through the x-ray as you can get asked for them but hold them loose, not in a pouch or wallet. Take your shoes off too even if they’re sneakers.
  • When you get through immigration in the US you head over to collect your bag from the carousel then head towards customs – hand in your customs form and generally just keep walking. They don’t take anywhere near as much care as Australia does. When through Customs you will head up a corridor and then (from memory) around to your left you can drop your bag for them to check onto the next flight so you don’t need to carry your bag to the TB terminal. This is your last chance to change anything from carry on to check in.
  • Both the green I-94W visa waiver form and the blue customs form must be completed without error. If you make a mistake, just tear it up and call the flight attendant for another one -- they're used to it. Samples of the forms are available here if you want to see what you're in for. The question relating to criminal records is question B on the back of I-94W.
    http://www.north-america.de/old/images/us_visum/i94w_front.jpg
    http://www.north-america.de/old/images/us_visum/i94w_back.jpg
    http://www.north-america.de/old/images/us_visum/cust_decl_front.jpg
    http://www.north-america.de/old/images/us_visum/cust_decl_back.jpg
    The bottom departure record part of the I-94W will be placed in your passport when you clear immigration. You must ensure that you give it to the check-in agent on the way out of the country, or you will be recorded as an overstayer. The check-in agent will often not ask for this.
• Find out if there's a shuttle to your hotel. It may take a bit longer but it will MUCH cheaper than a cab (generally) and you can probably book it for a return trip at a reduced rate. Get their contact numbers and make sure it's one of the companies with a lot of vans.

In the US:

• If renting a car, technicaly you require an international drivers license, but neither Amercian police nor car rental agencies will accept it and will instead demand the plastic one (this is also a legal requirement for them).
• Many Americans now feel the need to appologise for President Bush - let them but never personally criticise the president
• Do not discuss the health of the President in any way. Certain permutations of this line of discussion are a felony. Do not freak out when you discover how few white people work in fast-food restaurants. You should also have a few Spanish phrases handy for Florida. 'Tu madre es una puta' is not the right way to ask for directions to a hotel but you will manage to end up in a hospital.
• Phones
  • Never use hotel phones unless there is no other option
  • Avoid using an Australian mobile phone, unless your only other option is the hotel phone. Outgoing calls are the local carrier's peak rate, plus 30%. Incoming calls are Telstra's AU->US rate, plus 30%. Both are exempt from GST if that makes you feel better. :) Data pricing is even more insane.
  • Get a pre-paid phone card. You can get these off the internet, and they are not a real card. They are a set of numbers to dial, starting with a free 1800 number. $20 dollars and you will be able to make a good number of minutes of calls.
• Shopping
  • Jeans and sand shoes are particularly good. The shops to look for discounts are Kohls (pronouced Coles), or TJ Max. They have great sales -- what will be on sale is a bit random, and a much smaller selection unfortunately, but if you get something its worth it. Otherwise look for an outlet mall where lots of shops will sell brand names at a reasonable discount.
  • Electronics may not always be super cheap there, but it can also be fun to shop for it -- the shops are much bigger.
  • Books/comics are the other majorly cheap item. You save a lot on these. Borders is a completely different shop. CDs are usually about $15 US, which can work out a bit cheaper depending on what you want.
  • Outlet malls are the way to go here. You can buy a heap of interesting stuff from outlet malls and it's far cheaper than going to the tourist shopping areas with big, fancy stalls. The downside is you'll probably have to drive.
• Tipping
  • This is a black art - work on 15% (or double the state sales tax depending on who you ask) - 10% for poor service, 20% for good service. $1-2 per bag for porters (or carry your own).
  • another source says that this has crept towards 20%. If dining as a group of 6 or more, it will probably be pre-calculated and added to the bill. You may also have to add state taxes to the bill. Find a friendly local and ask or, if at a hotel, ask the concierge what the deal is.
  • You should make sure that you have a number of $1s and $5s to make change. Don't enter the country, if you can help it, with a load of $50s - it will be irksome trying to extract change from some people. The $2 is surprisingly uncommon in the US so if you get in one change, hang onto it as a souvenir.
• Generally you can survive on a credit card, but there are some places you generally can't use credit:
  • Taxis. These generally will take credit, but you may have to argue about it, so make sure you bring it up before you get in.
  • Some tourist attractions.
  • Some low-value food shops. You probably can use credit in chain stores like Starbucks etc, but you'll look like an idiot.
• Assume everything you see is tax exclusive unless otherwise stated. Tax rates generally aren't conducive to mental arithmetic -- Orange County FL (where Orlando is) is 6.5%, but that will vary if you cross county borders. Just wait until you're told the price.
• Legal drinking age is 21, but expect to be carded everywhere that alcohol is served, and be aware that the only acceptable form of ID is your passport (or a US-issued state driver's licence). I've seen guys with grey hair refused entry to bars for not having ID with them.>
• Food can be interesting. Biscuits are kind of like scones or muffins; if you want what we call biscuits then ask for cookies. Gravy is, well, see http://en.wikipedia.org/wiki/Image:Biscuits-and-gravy.jpg. Half-and-half is not good for you; it's half whole milk and half cream. Lemonade is lemon-flavoured water; if you want lemonade then ask for Sprite or 7-Up. What we call entrees they call appetisers or starters, and what we call mains they call entrees. Serving sizes are almost universally huge.
• Americans are used to living by rules -- in a country that big it's the only way things work. Don't try to break a rule, even if it's common sense, because you won't get people to see things your way. That even goes as far as jaywalking -- don't do it.