As if the limitations of DRM-crippled music weren't annoying enough, Boing Boing reports that the extra computations cycles necessary to decrypt DRM can actually drain your battery:

Playing DRM-crippled music will shorten the battery life of your music-player. Listening to DRMed iTunes songs on an iPod shortens the battery life by eight percent; playing back WMA-crippled files on a device from Creative Labs can knock 25 percent off the life of your device's battery. The extra battery-drain is attributed to the computation necessary to decrypt the files and verify their licenses.

The full article at MP3.com goes into detail about battery life claims of mobile music players.