Those figures are for training. Does not include mp. I hardly play mp since I beat people and move on. Plus, I never used my GC to play with friends. I only played MP in arcades, but my hours are all solo play.

Over 600 hours in GT4.

I'm going to GT5 Platinum... so I guess I will beat my record.

This gen I put in over 100 hours into Forza 3, Forza 4 and Gran Turismo 5 and I'm close to spending over 100 hours in Forza Horizon also.

Probably a tie between GTA: San Andreas and GT5.

Sly 3, Red Dead Redemption, Smash Brothers Brawl, Twilight Princess, Naruto Rise Of The Ninja Too name a few

BTW guys.

 I'm at 54,000 km in GT5 right now... that means 270 hours racing at 200 km/h.... I thing the avg. hours is bigger because most of time I didn't get speeds over 200 km/h.

Call me crazy, but my game is VVVVVV. It takes a lot of time to get more than 2 minutes on the super gravitron and beat the game in less than 18 minutes. I think I have spent 70 hours perfecting that game.

I regret nothing!

Edit: the runner up would be F-Zero GX. It's probably a lot more than VVVVVV but I can check the time on that game.

90 hours in Yakuza 3. I got every trophy except for mod a weapon and clear EX Hard. All I have to do is get those two and I've got the platinum.

If the question is overall time in a single game, I wouldn't know.  It could be Castlevania on the NES, it could be Brigandine on the PSX.  Castlevania takes me less than 15 minutes to beat the game without playing the loop, but I've put hundreds of hours into playing the game.  Brigandine I've also put several hundred hours repeatedly playing it. 

Mass Effect 2 I think, although you could make a case for that as an RPG. Otherwise, Super Mario Galaxy.

Probably gta:sa, tony hawk 2, or re4. While I did do some traditional multiplayer on tony hawk, most of the time was spent trying to beat each others high scores in single player mode.