I'm an active french user (plugin developper) of Xlobby, and some point on the xlobby architecture are really interesting... some other not (not really open).
Now i think that i will move from xlobby to another media center... So i am looking everywhere actually....
THe linux mce project is really interesting.
MediaPortal also (a lot of similitude with xlobby and, totally open-source, but on windows).
But it's could be very cool to have some of theses good features from these windows media center on linux mce...