Which Steam game have you got the most play time on?

portal

TF2 , more then 1000 hours

Garry's Mod with 1544 hours and counting :)

Garry's Mod almost 2k Hours.

It's BFBC2 for me with over 750 hours...

You people are sick.
Counter-Strike = 155 hours.

Garry's Mod.

TF2. I LOVE payload race!

Counter Strike: Source = 1203 Hours (THE REAL Counter Strike by the way.)

Terraria, around 40 hours.

Team Fortress 2, 68 hours.

ATM 53 hours in Fallout 3. Still have to finish it though, will probably clock at around 60

Dawn of war 2 and Dawn of War 2 Retribution (345 hours and 240 hours).

Team Fortress 2

2262.7 h

For me, top 3 games that I've played the most are:

1. Call of Duty: Black Ops Multiplayer - 357.7
2. Team Fortress 2 - 129.8 (still playing)
3. Fallout New Vegas - 114.1 (not playing atm, will play again when I buy the new dlc)

tf2

3355 hours in TF2. 2500 hours came from idling though.
Football Manager 2011 - 650 hours.

TF2 = 630 hours. And after that one Terraria my most recent addiction :D Got it about 1 or 2 months ago and in couple of weeks played more than 70 hours :P Awesome game!! Going back to it again soon.

TF2, 558 hours, rarely idling.

TF 2

TF 2,also seems the most played here,not surprised.

Tropico 4

Terraria with 74 hours.

Fairy Solitaire.

Mount & Blade: Warband 83hrs.