The "key generators" are all fakes. Some of them look like they work for a while because servers you have visited with a valid key keep a cache to let you in again. As far as we know, there are no real key generators. If there were, we would have much more significant support issues. We certainly will drop the CD-in-the-drive-for-single-player check in a future patch, that is our standard procedure after a game's primary sales are over.

I dug up this thread from Graeme Devine right before the Quake3 release talking about CDKeys.