It would be really nice if there were a way to prevent Media Center from importing keywords from external sources.
I have a small list of keywords I assign to files which are actually meaningful, however recently I have noticed that a number of podcasts I'm subscribed to are now including keywords in their metadata, filling the list with junk information.
Similarly, when "Get Movie & TV info..." grabs data for new files, they include the worst keywords imaginable, with things like "Duringcreditsstinger", "Ice Cream Truck", "Cousin", "Title Based on Shakespeare", "Leave", to name a few from the last handful of films I imported.
Oh, and I've already managed to clear all my library's keywords once in the past when I was in the wrong maintenance view and didn't realize I was working on all files rather than only my videos. The previous backup was days ago, and it was less work to re-tag all my audio files (though I keep finding ones I missed...) than restore a previous backup.
I now know that I could probably have manually created a backup, restored the old one, saved that data to an MPL Playlist, restored the manual backup, and selectively imported that data, but that's still a huge amount of work.