Good Question!! I'll have to go back thru my archive to see what the longest game actually is, but this one is certainly a contender:
http://www.chess.com/echess/game.html?id=16894759
We started it on March 15th, and we JUST called it a draw on January 1st. (9 1/2 months)
When I get the chance, I'll go back and see what else I can dig up. I'm sure I have several that lasted more than 6 months tho.
WOW!!! Yeah, 1-year today!!! And the 2 of you still have another whole game to play after this one!!! 
I don't think ANY of mine have taken a whole year. My Dark Knight Tournament is over a year and a half now, but that's multiple rounds. I've never seen a single game take over a year before!!! And you're only on move 38!!! That's actually taking the full 10 days (9.6) per move!!! He SHOULD be a turtle!!! 
We called it a draw after 1 year and 2 days ;)
Basically, if he doesn't check me, i mate him, and he can continue to do so forever. I thought it would be unsportmanslike to go for the 50 moves rule.... 
I think we have a new winner. This game started on June 9, 2008 and is still going:
http://www.chess.com/echess/game.html?id=7390993
Nice one!
Though I must ask myself: are those players of flesh and blood? A 3000+ rating always makes me a tad suspicious, the stalin pic and alleged birthdate even more so. I could be seriously in the wrong of course, but players of that level would (should?) be known - not only on their local chess scene, but wider as well.
Hi Chessmate,
No need to defend your longer time-frame, this is the forum of the chess-turtles afterall! And I hope you were not offended by my comments - the problem is, there are dubious cases around, and for the normal user it is next to impossible to tell which is which - sadly.
Anyway, best of luck in your game!
Congratulations. (ok, only a draw, but if a chess.com rating means anything at that level the opponent was 200 points stronger).
Now onwards, 2 years and 2 months is the target to beat!
Getting the draw looks even better now, chessmates, since it appears you were playing against a computer. You were right Dr.Phil, his opponent was NOT flesh and blood (who could honestly have a rating over 3000?). capablankamonte's account has been closed for cheating.
http://www.chess.com/groups/team_match.html?id=15681
I have this game over here, been going on for a year and 4 months.
Main reason for me to join this group
We had a thread before about the longest game of correspondence chess ever, but what are the results when we only look at chess.com? What's the longest game a turtle has been in?
In my case, this game is still ongoing: http://www.chess.com/echess/game.html?id=15360690 has started on february 17th, 2009 and at this rate it might hit the one year mark... (mainly due to my opponent by the way, he should be an honorary turtle as he's even slower than i am, by a considerable margin.). The situation looks drawish to me, so it might be going on even longer...