I have not used Vista, but heard that it contained DRM measures that can make legitimate computer use more difficult. For example, from this article:
Certain high-quality output paths--audio and video--are reserved for protected peripheral devices. Sometimes output quality is artificially degraded; sometimes output is prevented entirely. And Vista continuously spends CPU time monitoring itself, trying to figure out if you're doing something that it thinks you shouldn't. If it does, it limits functionality and in extreme cases restarts just the video subsystem.
So: what about Windows 7? Is there anything you can't do with it specifically because of the DRM that's built-in?