It's a Windows Media Center plug-in that's simplicity itself to use. Just click on the Boxee option in the WMC main menu to close WMC and open Boxee, and when you're done watching your content just close out to automatically bring up WMC again. Even better: the switch can be made with your remote, so you never have to leave your La-Z-Boy.
I would like the integration to go the other way. Have a Boxee app to see guide data from MC to remotely schedule recordings and ability to view MC recordings, conveniently saved to a separate NAS, with subtitle/closed captioning support (this is currently not working). Then throw all this onto the upcoming Boxee Box and add integration with network tuners such as Silicondust's QAM box and upcoming Cablecard box (silicondust's drivers have network sharing / conflict resolution support). And now we won't even have to look at MC directly and Boxee is like an unofficial MC Extender that will probably get 1000% more support than the official ones.