DRM keeps SOME people from pirating it. While a lot of you would scoff at the notion that pirating games is hard, there are some people out there who don't know how bittorrent works (or even what it is), and the whole notion of copy-pasting exe files is scary and foreign to them. DRM, even simple DRM, stops these people. If a game had ABSOLUTELY NO DRM AT ALL - as in, you could give your friend's the CD and they could just install it like that, piracy would increase for that game. Just look at World of Goo.
I am not against simple DRM designed to stop the very lazy pirate. I am against intrusive, potentially system damaging DRM because it doesn't stop any more piracy than simple DRM. Simply put, the same amount of people who would be deterred from pirating a game with heavy, intrusive, complex DRM is almost exactly the same amount of people who would be flummoxed by a simple CD key. A determined pirate, on the other hand, will not and CANNOT be stopped by ANY type of DRM - look at Ubisoft's new fangled on-line DRM - it didn't stop the pirates from cracking it, now did it?
So please developers - put simple DRM on your games. You won't stop the determined pirates, no matter HOW complex you make your DRM. Without quantum encryption (which isn't as far off as you might think), there is no such thing as fool-proof DRM, because no matter how many checks you introduce into the game, a programmer or a cracker can just EMULATE the info needed to pass the checks, or hell, remove the DRM altogether from the program!
Simple DRM is all that is needed. I will grant you the fact that you do need to deter the lazy pirates, and simple DRM does do that. But the harsh DRM is overkill - it's unnecessary, it takes money for you to design and modify in an ever-lasting war against the pirates and it can hurt your paying customers.