No taxes, no credit card, no...nothin' really. The dealer asked if I was 18 or over (I'm 30!), and then at Enterprise they asked for my DL. I was surprised b/c I remembered your thread and how you had to present a credit card, etc.
And no, I don't think there is any time limit to it. I'm sure if, after a few days, they cannot return my car to me they will opt for a loaner. They just happened to be out of lot loaners (or so I understood) this morning.
The process was very simple. Like I said, there was a short wait for Enterprise to pick me up, but I was out of Enterprise in less than 10 minutes.