I have stalker on steam, but I've never downloaded or installed it. But I noticed last week that the Backup option gave me the choice to backup a Stalker Ownership Check. Wondered what it was, and then forgot about it when i started playing bioshock.

I think it means that the Ukrainian military is onto us. They're tracking everyone who owns a copy of this game to see who is actually an illegal Zone-poacher.
"Report all instances of STALKING. Do not let de looters hide behind your back. Dey bring raidioactive eye-tems from de zone which are very dangerous to human health and life. Only with your help can we eradicate dis heedious phenomenon..."

Yes. Same with me.
If it is anything of which has been thorised, I hope it is the massive deal off theory.

Um, I have STALKER but it's not installed.. but the ownership check is..

Just a question: does the retail box version require Steam?

Can't speak for CS, but SoC and CoP do not require Steam (and I suspect CS doesn't either).

Ok, so, next question: why do you all bother buying it on Steam??
The game is pretty recent, and the box version can be found everywhere.
You buy it on Steam cause it's "sodamncool-with-socool-achievements", or... what? Or maybe it's a question of price?
Tell me, I don't understand.

Ah, so you are just looking for an excuse to bash Steam :p
I bought the retail of SoC and loved it. When I saw it on sale two months ago, I grabbed the Steam version for dirt cheap. And I go CS dirt cheap too. Why? It is more convenient, since it tends to take less time for me to download a game from Steam than it does to find the disc, install it, and patch it.
Got CoP retail, but I'll probably re-buy on Steam if it is ever under 10 bucks. Again, convenience.
And none of them have achievements.
Plus, there is the same benefit digital distribution has over retail: It is easier and faster to buy online than in a store.

Whoops. Disregard this,

It's a 33% discount if you own both the original Stalker and Clear Sky. Only 19,99$.

Because I paid under five dollars to get it and I don't need a bunch of discs with crap that could be on my hard drive instead.

Because I've got over 3TB of HD space, but only about 24" of shelf space.

Minor correction: You only need to own Shadow of Chernobyl or Clear Sky.

It is only $10 in here what a great deal.

What?