well, that largely depends on the game and the genre that the game falls under. for the past year or so, i've been playing mostly single player games in large part thanks to Oblivion and recently NWN 2. however, that doesn't stop me from getting online with games like Quake 4, Halo, Far Cry, E@W, or Medieval II: Total War.
MMO's are out of the question: i don't really like the concept, and i don't really like all the fee's that they want to tack on.
See the struggle of the faithless lot as they negate their time
How low to sink to the depths of their frame of mind