I find I do best playing 3 tables at once. I play conservatively and don't see a ton of flops so playing 1 or even 2 tables I get bored out of my mind. Playing 3 seems to be perfect because I can handle it even if I'm in the middle of playing 2 or 3 hands at once (if I get good hole cards).

I have played 4 from time to time (especially during Lucy Jones) but I find that when I do get a run of good cards it can be really hectic trying to make decisions on the turn or river on 3 tables at once! The other thing I've noticed is that when you have the time to make the quick bet with little or no hesitation it usually works out better for you than when there is a long delay (while i'm deciding on another table) before you check or bet....it can make you seem weak even if you're strong and then you can get outdrawn.

I find 3 tables perfect because I can pay attention to the tables enough to have a good idea when someone is bluffing, on a draw etc and if the opportunity arises I can take a stab at stealing a pot when it appears no one has hit. With 4 tables the action is so fast and furious I just can't concentrate enough so I think it costs me.