Cory Doctorow talks to Microsoft about DRM:
"The same thing happened to a lot of people I know who used to rip their CDs to WMA. You guys sold them software that produced smaller, better-sounding rips than the MP3 rippers, but you also fixed it so that the songs you ripped were device-locked to their PCs. What that meant is that when they backed up their music to another hard-drive and reinstalled their OS (something that the spyware and malware wars has made more common than ever), they discovered that after they restored their music that they could no longer play it. The player saw the new OS as a different machine, and locked them out of their own music. There is no market demand for this 'feature.' None of your customers want you to make expensive modifications to your products that make backing up and restoring even harder. And there is no moment when your customers will be less forgiving than the moment that they are recovering from catastrophic technology failures.".
He goes on to describe how the same thing happens with iTunes when you buy a new Mac every year. There's a pretty PDF version here