I played my PSR2000 at a similar piano bar type situation Friday night, filling in for a friend. There is a BIG tip jar on the pianobar. At the end of the 3-hour job, there was $187.00 in it. A lot were for requests, but at least as much were just tips.
I try to do all requests regardless of whether there is a tip involved, but I must admit I assign a priority to them.
My son in Tulsa called just this morning to tell me about a dueling piano setup there.
They did it as you described--all requests were tips. He said they must have had a thousand bucks in the jar.
Since I started doing the piano bar at the other place about a month ago, I've had a lot of interest and a couple of offers to do it elsewhere. Maybe we're on to something. I thought the piano bar scene was pretty much extinct around here, but it seems it was only dormant.
Let me warn you--you had better be really versatile before trying this type of thing.
Friday one guy kept requesting Sinatra songs (at $5.00 a pop). I think I did about 10.
Another was a Merle Haggard fan, and so on. It is fun but, as Dave said, very intense.
DonM