Not sure about hotels, but at T-Mobile HotSpot locations, such as Starbucks or Borders, you just fire up your browser. When you try to go to a website, you'll first be brought to the T-Mobile homepage, where you can set up your account. I forget the prices, but it's X-dollars a month or like $6 an hour.
After that initial account setup, you just put in your username and password, then surf at high speed. They debit your credit card automatically each month and you can see your monthly statement online. You don't actually get anything in the mail, if I remember correctly.
On subsequent trips to HotSpots, the T-Mobile welcome page, where you enter your username and password, only comes up once a session. And you don't even have to bookmark it, b/c it pops up automatically, no matter what site you try to go to first.
It's quite a novelty and an awesome convenience if you don't have high-speed at home, but once I got my home network up and running, I haven't used a HotSpot once. Why pay somewhere else when you have high-speed at home?
Lastly, if you go for the $6/hour deal, watch the clock. There's no warning about your time, AFAIK. If you go one minute over, you're payin' for that entire next hour!
Good luck!