I usually only go to around 4 or 5 per year (NYCC, AnimeNEXT, Otakon, Anime Boston, and Connecticon). But I also now go to renfairs and various cosplay meetups.
I was supposed to go to 10 cons this year because my friends went to colleges near cons, but now I'm not sure that I will have time for that :P
But I believe that you can never go to too many cons! lol as long as you have the money for it