Gabe Newell has deep pockets, sure, but "too good to be true" usually means "too good to be true." If you receive an email from Steam Community saying that Valve has gifted you a free copy of Far Cry 2 on Steam, make sure you steer clear.
The scam works like this: Steam users will get an email from a fake email account that has a bogus "[email protected]" address. The email will then ask you to go to the Steam Community page to redeem your prize. Click through and you'll be forwarded (if your browser doesn't catch wind of the scam) to what looks like the regular Steam Community site but is really just a nicely done facsimile. When you log in with your username and password, the site will scoop up that info and deliver it to the scammers to use for whatever nefarious aims. The giveaway is plain, if you're paying attention: the url reads "http://h1.ripway.com/steamedcommunity" when it should "https://steamcommunity.com."
Pretty devious, I'll admit. Phony email addresses are the oldest trick in the phishing book these days, but going the extra mile with the fake site and luring people with the promise of free stuff, well, that's downright dirty. Me, I would've turned away the second I read Far Cry 2. Free Bejewled Twist? Yeah, those theives would probably have my account by now.
So, Steam users: delete any emails about free copies of Far Cry 2, and be wary of sites with obviously phony URLs. If you do get suckered, consult Steam's knowledge base on what to do next.