I was just wondering if and when you select a game to play when using steam, and then it downloads the steam install. Does it register the CD key you have to the acct you are using on Steam?
I picked up a copy (In Canada) of the European version new for 24$ canadian (18$ US). Also, I was at EB Games, and I saw a copy used for 10$ (7.50$ US), so I bought it and gave it to a friend. Since CD keys are registered to the account, I didn't have to worry about whoever sold the used copy cheating us, since once my pal registered the CD key from his new used copy, it was his forever.
Anyhow, buy it. It's cheap. For 7.50$ US, my friend got Counter-Strike, TFC, DoD, and most importantly, Natural-Selection. And a host of other mods like The Specialists, Hostile Intent, HLRally, etc. Not a bad buy for 7.50$ US.