At least that's what Random House has concluded after doing a study on it's audiobooks sold with and without DRM. Here's an exerp from the AnythingButIpod article:
"The really interesting part of this story is the experiment that Random House conducted on piracy. They sold DRM free books online and water marked them to track them on P2P networks, but what they discovered was the pirated copies on these networks were from ripped audiobook CDS and cracked from DRMed audiobooks. Legitimately, purchased DRM free audio books did not show up on P2P networks. Random House concluded, “Our feeling is that D.R.M. is not actually doing anything to prevent piracy.”"
Wow. Sell people what they want, the way they want it, and for a fair price, and they won't pirate your stuff. Amazing concept. (Can you sense my sarcasm?) The entire NYTimes article is here.