Don't know about single player but multiplayer on Bad Company 2 has cost me approx 500 hours of my life! My time spent on BF:MC must easily be double that.
100%ed GTA Vice City and San Andreas, but couldn't be bothered with GTA IV. I dread to think how much time I wasted driving people round in taxis and looking for hidden objects. I can't remember how many hours, but I know it was an entire summer for one of them.
Trying to find the final car in LA Noire I had to park and wait on a street corner for it to pass! So I'm sat in my virtual car on a street corner for at least half an hour. Art imitating life or what?!