Wut 75+ hours? I suspect some games have taken me beyond the 1000 hour mark. But who keeps counting when it takes many years real time? ;-)
Ultima V, and Bard's Tale III were probably some of the most time consuming ones. In real time I think some of the old Infocom adventures hit the record, with 10 years from purchase to completion but the effective game time of those are pretty low in comparison.
Most replays probably goes to the original Civilization, well beyond 100 games. Damn you Sid and your "1 more turn" philosphy.
Of games newer than 2000 I guess GTA:SA was one of the longest. That game just never seemed to stop, and it was a fun ride all the way.
Some great time stealers that couldn't quite make the top of the list:
Grim Fandango, The Longest Journey, BG1 and BG2, X-Com:Terror from the deep.
*Insert comment about short attention span of the youth, and superficial modern games*
*Also bottom of a frozen lake*