This is the constant bane of our lives when in the State....but we've gotten used to tipping only because we hang out with our relatives and friends and have learnt from them.
When we're at hotels that provide the "dumb porter" (the trolley), we normally manage our own bags. It's also pretty obvious to the porters that we are self sufficient if we are wheeling the bags into the hotel by ourselves - by and large, if we've got our bags under control, they leave us alone. If we use the porters, we normally tip about $1 per bag or a maximum of $5.
At places with counter service e.g., McD, coffee shops, cafe's that have a tip jar near the counter, we normally leave about $1 or $2 in the jar; if the service at the counter is prompt and if the person was friendly and if we are buying lunch/food. If we're just buying drinks, snacks or coffee, then we leave nothing. My husband, who goes to the states 2 or 3 times a year for work, will drop some coins in for buying drinks. But when I travel with him, I normally break this habit within 2 days.
I expect that most of the other Aussies reading this thread will probably provide their input as to whether they leave anything or not.
At sit down restaurants with wait staff, we normally check the bill and look out for the sales tax. California sales tax runs at about 8 - 9 % and the sales tax amount is based on the cost of the food only. If the service is good, we double the sales tax amount. This means that we are leaving about 18% tip. If the service was sub standard, we leave a minimum of about 15% tip. If the service was above average, we leave about 20%. Good service is when the waiter is charming, takes our order promptly, comes round to refill our water without being prompted, is patient with our child and generally comes round more than once AFTER taking our order (they normally stop by once to check - this is standard service).
We NEVER base our tips on the total amount of the bill, which includes the sales tax amount. Doing so will mean that they get tipped more than 20%.
I think NY sales tax is about 7.5%. So over there, the minimum is 15% if we double the tax amount. Be aware - that if you leave LESS than 15%, you may encounter sarcasm and outright rudeness.
I think FL sales tax is also in the 7's.
The bill should show what the % sales tax is - if not, we will ask the waiter and find out PDQ so that we can work the tipping out.
We have tipped housekeeping - generally about $1 a day - if they have been good and for longer stays. They normally leave their names and if we find we have consistently gotten the same housekeeper for more than 5 days, we leave a tip (usually at the front desk) at the end of the stay; rather than in the room). If we stay for 2 or 3 nights, we never tip housekeeping. We have occassionally bumped into our housekeeper doing the rounds and if we do so, we chat and then tip them personally. Remember - we tend to do long stays in the same hotel in Silicon Valley and are on first name basis with some of the housekeepers; so this may not be the norm for most Aussies travelling.
We have also tipped taxi drivers/chauffers - but only after checking what the bill includes. Some of the hire cars include the tip in the total amount; so we always check to see if this is the case or not. With taxis, it is always easy to see if tip is included as you can check the meter. Certainly we found with the NY taxi that took us to the airport that the breakdown included meter amount, baggage portering and tip. We certainly weren't going to add an additional tip on top of this!!
You may also find a tip jar in the courtesy buses that the car hire companies operate that take you to their sites. Unless the bus driver helps us with bags, we don't leave any money.
When shopping for clothes or stuff in stores, there is no tipping. Just remember that the sales tax is added when they ring up your purchase at the counter (it's not included in the price tag).
One other thing about shopping for stuff in NYC - if your total purchase for that transaction is under $150, you won't be charged the sales tax. This was the case in 2007; so I waited till I was in NY before hitting Victoria Secrets, Gap, Banana Republic, Zara, H&M, department stores etc.