I've recently upgraded from many years of Media Jukebox use to Media Center because I finally implemented the HTPC and Networks in the condo. It is intended we will use the 1080p Bravia in the front room to view movies from our wifi'ed database of movies ( DivX ), of course play the music library which is heavily tagged and view our library of digital pictures.
While working on these files at my computer the interface is all wonderful. The questions arise when moving into the front room to enjoy the spoils of all that work ;-)
I think that for most family members movie selection and viewing in the Theater mode works great. Simple selection if you already know what you want of music is OK. And pictures work fine. My requests for display during music playback I'll leave for another topic.
What I find hard to work with is a mixed media library. I use lots of playlists to describe the media and select unique collections on the fly. FOr a picture I might have playlists for picking out pictures of grand babies, which were in a park and are from the last two years. These playlists are meaningless for the movies and the same can be said aboutmovie playlists and the hundreds of music playlists which have been created.
It would be real nice if playlists were specific to the media type. Then I'd use a single library and it would flow nicely with the theater view and use in the front room. Currently I defaulted to using unique libraries for each and that is usable but we lose many features of the flow the three media type buttons provide.
So that's my suggestion, I'll end with saying that I really do love the Media Center. I find the Windows Media Center to be completely unusable, and there has never been a music jukebox to top the features and functionality.