There are rumours that Microsoft's Windows Genuine Advantage servers have failed. XP and Vista users are reporting their operating systems are being incorrectly marked as pirated and then rebooting in a crippled state. This problem may continue for days.
I can think of problems with activiation servers going back at least fifteen years to the bad old days of Unix site licenses. Somehow the site license server was always the brittle component. But for Microsoft to accidentally break millions of customer's computers, well, that's astounding. Hopefully the problem isn't as bad as it sounds.
See also: Google Video breaking the right for its users to watch the videos they bought. DRM is consumer hostile.