.. Automatic Metadata, since I think a more hands-free, user input NOT required system is better all around.
However, the biggest thing holding me back from using it more is the TV experience. It's really not very usable. 2-3 times more clicks to do stuff than other products, non-intuative interface, general lack of refinement.
For example, I can't order scheduled shows by priority (1-15), only High, Medium, Low. Conflicts in scheduling are not handled gracefully, it doesn't ask me what to do when I'm done watching a show, among many other issues.
Use any other product for awhile, and the shortcomings in the MC TV experience are pretty glaring.
Since I can't use it for TV, and the wife enjoys watching TV, it's not used nearly as often as WMC, which is an inferior, but more usable product.