I only recently bought steam copies of the games so more than 90% of my stalker time is with my DVD copies so I can't give actual hours played however I have been using the Steam version of COP to play with the Misery v2 beta and it is currently at 135 hours. But that's a blink of the eye up to my main play time. I'm pretty sure I could be in double figure months for both CS and COP. Not as much for SHOC but LA will probally help it catch up.
Everything you want to know about Degtarev's zone is in the: COP Survival guidehttp://cop.zsg.dk/
Played Soc since release , and Clear sky too i have many hours put into those 2 games , while CoP didn't amaze me i didn't play it too much. I dunno why Clear Sky is my fav at the same time so is Soc. .
Constantly switching between those 2 games.
I have beaten all three titles once. It took me nearly 6 months alone to beat SoC after release. Currently on a second playthrough of CoP with Misery. I like to do all the side quests and explore everywhere so full playthroughs take me forever. This and between my work and other life responsibilities leaves me with little disposable time anymore.
All said and done I can say that i have clocked more hours in Stalker than any other games between '07 and now.