Originally Posted by The Dark Side
You should play as many as you can while still being able to follow the action and make informed desicions.
^^^ Pretty much this.
If 2 is your comfortable max, don't try to push it. Most people mess up with multi-tabling because they add too many tables too quickly. I've been guilty of this myself. I used to play 9-12 FR tables regularly, occasionally 16. I could handle them just fine physically, but my game started suffering from the burnout-inducing level of attention required. It started to be more of a chore, and I would finish exhausted even if I had a good session. After finally diving into a deep downswing, I took a break and decided when I came back, I'd start much smaller. I know if I took my time and had the patience to work my way up slowly, results would likely have been different, but I moved too quickly. I had a false confidence based on my ability to physically react to that many tables, but my mental game had not developed the stamina to keep it up while making good decisions. I'd argue that the mental aspect takes a lot more training than the physical ability to move the mouse and click buttons fast enough.
I now play 4-6 tables at most -- usually 4 or less -- especially when playing tournaments (either MTT or SnG). This gives me plenty of time to enjoy the game and also keep up with my opponents, without feeling as rushed. My results have steadily improved since my downswing. Gradually I may add some tables, but each progression will be much slower than before. I'll basically wait until I'm bored with the number I'm playing, rather than pushing to add another as soon as I think I can handle it.
I will add that multi-tabling tournaments is a lot harder than multi-tabling cash, at least until you reach the push/fold stage. With cash games, you should be playing with a full stack always and the blinds don't change, so multi-tabling cash is a lot easier in that regard. The added complexities and multi-stage play required in tourneys, especially when your different tables vary greatly in levels and stack sizes, just make it more difficult to keep up with. If you're going to start out multi-tabling tournaments, then you should start with sets, i.e. starting them at the same time and not adding new ones in the middle of the set (this is much easier with SnG's obviously since they fill frequently and constantly, versus intermittently scheduled MTTs). Also not mixing regular speed and turbos. These approaches keep the levels somewhat synchronized across the tables, until you are confident that you can properly shift gears between different levels going on at the same time.