A few. It depends how I'm playing. If I feel like I'm just getting unlucky than I usually stop after 1 or 2. But if I'm playing solid poker and I know where my mistake was than I usually play a few more. If I ever lose 25% of my bankroll in a day than I am done. I don't care if I'm playing well or not, thats a lot to lose and I just need time away from my game.
Usually if I'm doing bad on one site I'll go to another site that I have money on. To me when I lose it doesn't bother me as much as it would bother other people. I don't deposit online and have built bankrolls from freerolls
alone so the money isn't as painful to lose even though I don't like to lose.
Good luck at your tables