Apparently, Valve knows if you have been naughty or nice. I don't know what's gotten into them, but you can count your lucky stars if you were using cheats on Valve and didn't get banned.
Valve just updated their Steam Hardware Survey this week, and on this occasion, they decided to collect some new data from Steam users about their computers. Also, a new Valve Anti-Cheat technology was implemented this week, and as you can imagine, more than a few users were caught cheating.
Over 10,000 users were using some sort of enhancement in order to improve their gaming skills but they finally got caught and their Steam accounts were banned permanently. Most of the cheats were used for Counter Strike: Source, but other games were not left out either.
I'd expect that this ban is permanent, in comparison with WoW accounts bans, which expire after a month or so. This anti-cheating measure seems more than appropriate on behalf of Valve, as they further expanded their online distribution system over the past few months, making available via Steam a lot of games including the Call of Duty series, Dark Messiah of Might and Magic, RoboBlitz and the Civilization series.
Furthermore, they plan on releasing next week via Steam, the WTCC official game, RACE and a single player version of The Ship.