If your computer can still keep up with what you want to do (I'll take a guess that you're a gamer?) then in a way it's silly to upgrade for the sake of it. You didn't mention if it's the E6600 or the Q6600, if it's the E6600 then you might consider upgrading to quad core in the near future as more games make use of that. If it's the Q6600 then your system should be more than enough to keep you going for a while longer (unless you're playing with a seriously high screen resolution). 
im running at 3.2... well i was until i got onto windows 7 it seems to get unstable every month or so. could do with some bios tweaking but dont really get much spare time after work and not really sure what id do, its on 3.2ghz on air
