How long do you play it?

Well in 1 session probably 8hrs. If the game is good though I will never get bored of it.

As if this needs to be said, it depends enitrely on the game.

First day: 3-6 hours
Second day: 2-5 hours
Third day: 1.5 - 4 hours
If I still like it, then .25-2 hours per day until:
1p game: Game is complete
Multi: 3 months, then come back after another 3 months.

My tolerance for bad game design has dropped sufficiently over the years that I now quit playing when the culmination of flaws in a game get high enough that it frustrates me enough to turn the game off in a rage. As long as I never hit that point, I don't get tired of a game until it's just too tedious to keep playing it. And that can take a very long time indeed. No exact numbers for you, because as has already been pointed out, it varies immensely from game to game.

Couple hours..If i have time..

As long as the game is good I can play for hours on end.

Something between 5 minutes and 1000 hours (I have spend more than 1.000 hours on Oblivion).

Depends of the game...

I have near 350 games in physical media, and I can tell you that the majority of the games are unfinished or played less than 1 hour.

But Nintendo games: oh, thats a different story. I love every Nintendo game... characters, gameplay, etc... I do finish every Nintendo game.

I once played Diablo II for like 11 hours straight... (I am never going to play an online RPG again)

I could see oblivion become the game I spent the second most time on... (Diablo 2 would be #1... I put over 500 hours into that)