Tell me the Game on which you have spent the most hours on steam. xD

Team Fortress 2 = 1,095hrs

CSS 2500+

Team Fortress 2 with 920 hours, then ArmA 2 with 300 + 100 + 89 hours in it.

On steam , TF2 550 hours
Off Steam , COD4 , San andreas , WoW , over 3000 hours combined .

TF2 - 1,246.4h

Tf2 with 269

Dungeon Defenders - 4023 hours :)

I have an embarrassingly large amount of time spent in L4D2. I don't even like the game anymore, put I keep getting dragged into it.

Mount and Blade Warband(With its dlcs and mods) around 770 hours.

Defense Grid 144 hours. Wanted to see how close I could get to 100% completion. Knew I'd never get there but was pretty close until they added new achievements for Containment.

Garrys mod 70 hrs

Highest would be Skyrim with 525 hours. But only maybe 25% of that is actually playing the game... the other 75% was screwing around with the creation kit, building mods, testing out other people's mods, etc.
Second highest is Borderlands with 67 hours.
Third highest is a tie between Just Cause 2 and Legends of Grimrock with 26 hours each.

399h Mw3... :( it was my first CoD FFS ^^

80 H on TF2. It wont be so big, but the loading times on my netbook..... thats like 2/3

Spiral Knights - 291 hours
Call of Duty Black Ops (SP) - 254 hours
:3

Fallout 3 GOTY 106.6 hours
Orcs Must Die! 2 84.4 hours
King's Bounty: The Legend 38.5 hours

But HoMM series & UT series are my most played games ever. Easily over 1000 hours with each.

About 1900 on tf2 :)

(plus another 400 on another account, always tf2)

Ive got 102 hours on Skyrim, the last time I played it properly was the start of last year.
My save corupt when my character was level 50ish, I had maxed out a few of my stats, and I was barely half way through the main storyline :(

55 hours on dungeons of dredmor.

http://steamcommunity.com/id/gk99/games?tab=all

Probably cs 1.6 way way before steam was tracking time...

DOTA 2, 1k+ hours.

My top 3:

Dota 2 - 400.4 hrs
Team Fortress 2 - 336.5 hrs
The Elder Scrolls V: Skyrim - 158.8 hrs

1600+ CS 1.6 but i played much more, steam is old bro and this feature is newb