Boxee is okish... there are some really nice features vs mediaportal, however I find it tries to do a bit too much automatically and there's no way to check progress of media folder scanning, or adjust any thing it thinks is correct that isnt... at least that I have found yet. It seems to drive my PVR box into heavy load for something as light as a youtube video (and some others too) which causes the system fan to blast full speed... mildly annoying. Add that it only uses about 6 buttons (that I can tell) off my Windows Media PC remote. (mediaportal uses nearly all...) I do like the amount of apps it seems to have available, including Joost which I used to use, but since it didn't seem to like me using the remote only to control it, stopped using it. Boxee also doesn't use the LCD display on the front of my mediaPC, something Mediaportal does with a lot more configuration options (yes this can be frustrating too, I kinda wish it were more like the Boxee it just should work without configuring or updating codecs all the time) During my messing about with it yesterday I managed to crash it 4 times in a few hours. Also some of my videos such as Family Guy, South Park, etc seem to show up square in my screen (it's a normal, non wide PAL CRT TV...) with black bars on both sides I wonder if this is to do with the videos being NSTC. This is not how they are in mediaportal... I run my Windows XP at 800x600, which is the best that the TV will do, there is no other monitor hooked up.
I should give XBMC another test and see how it runs now. There are so many of these TVmediaPC apps these days it's hard to find out what's truly best.