I haven't seen a situation where they completely lock an account full of games, where the person who purchased those games can never access them again. The guy above is being overdramatic.

They CAN "VAC" ban your account, though. That does not deny you access to your account in any way, and will not prevent you from playing the games online or offline* as much as you want. The VAC part of the ban is that you cannot use any Valve run servers on games that use Valve to run their servers, like TF2, DOTA, Counterstrike, Left 4 Dead, etc.

You can still play the aforementioned games online, BUT after the ban you can only play on non-VAC secured servers (aka player servers that are more likely to have rampant cheating). The ban DOES NOT remove the game from your account, delete your account, block your access to the offline portion of the game unless, I suppose, the game has an always online element that uses VAC.

*One of the annoying DRM "features" of Steam is that you can play any of your games offline as long as you log in online at least (I think) once a week or so.