well, for everyday app. a dual core will be more than enough as more apps still dont use 4 or 3 cores yet. maybe a few years down the road apps will use quad cores.
For gaming, i would actually have to say go to a tri core cpu (like phenom II x3 720). Yes most games only use 2 core, although that extra third core can be use for background task, OS, drivers, ect. This will make more breathing room for the 2 core that you are use for the game.