No idea. I know I spent a good deal of time on Pokemon Gold, as that was my only portable game for a while and I loved it, but not nearly as much time as my peers. Probably more than 50 hours, but I'm not sure.
Spent alot of time passing around Advanced Wars with my buddies back on the GBA.
Spent a ton of time on Oblivion, I think I was reaching 50 hours. Sold it in since then and have been meaning to grab Shivering Isles. My time with Oblivion is far from over (I hope).
Orcarina of Time has at least 50 hours in the first couple play-throughs, and I've played it a ton since then. Same with Link to the Past.
Spent tons of time on Halo back in the day, co-op and multiplayer CTF on Blood Gulch. Definitely more than 50 hours. Goldeneye, too. I still remember scraping together my money to get an N64 after playing that game.
Spent a ton of time on Halo 2, as well, online matchmaking. 50 hours easily.
Then there's StarCraft, which I've been playing for years, and could never accurately gauge how much time I've spent on, especially taking into account time spent in StarEdit making various campaigns and UMS games (which I got pretty damn good at back in the day).