I personally play my best when playing 6-8 tournaments... for me this is just enough to make sure I pay close attention, but not so many where my attention is spread too wide. I can play up to 18 or so tables but at this point I'm in pure auto pilot mode and the volume is definately causing me to not make optimal decisions and also I am sure I miss alot of spots where I could be chipping up. Find what's comfortable for you and stick to that... Everyone plays their best when comfortable.