Speaking of feeling bad for the waitress since you took up two tables and only bought drinks, did you think about the owner of the establishment? I think you need to send $100 to make up for the food you should have bought. I'm sure that the company would appreciate it.

I see these type of guilt threads all the time, about the maid, the valet, the servers, skycaps, etc. People denounce their cheap friends, and at the same time, overtip, which in my eyes is just as bad. In fact, $4 on a $25 bill is 16% tip. It's certainly not your fault that the place was busy and you couldn't get a seat at the bar.

I have gone out with people who left $1 for a $40 bill, which wasn't appropriate. I added to the tip, and made it fair.

Servers know what their pay is. They do get tips, and I'd guess than a good server in a good restaurant makes $12-$20 an hour. In fact, I go to some mid level chains (PF Changs, etc) where servers make $200-$250 in tips for a 5 hour shift.

I had a friend in high school who worked at a Baskin Robins who made server wages, at that time, since they might get tips. Now, that was certainly a rip off.