I just received my free Media Centre key, put it in the box, and hit next. Several minutes later Windows suddenly restarted without warning, then restarted a second time (sudden, but an OS restart, not a hardware restart).
When it came back up all of the items pinned in my taskbar have been cleared and the defaults returned, Steam has been corrupted (and is repairing), iTunes has lost a lot of settings, and even Chrome wasn't able to recover the tabs I had open.
So word of warning, shut down EVERYTHING before you install Media Centre. You still might see your Explorer settings reset.