I can second this. MP is really great if you have an extensive collection of video, tv-rips, photos and/or music. Only thing I haven't been able to do with it well is web-streaming (NetFlix, etc.) I use Boxee for that.
Setup and media indexing is pretty simple, if a bit time consuming. There are several good walk-throughs on the MP forums.
I have it running on my HTPC, and even my wife is happy with it in the living room. As far as XBMC goes, MP is a fork from a couple of years ago, so they have a lot in common. I've found that the movie/tv-show handling is better with MP, especially with the Streamed MP skin.