I've found that the inbuilt media player has a lot of trouble playing my video files. All video content I have on my machine, which is running ubuntu 8.10 btw, plays without a glitch on vlc or mplayer.
I'd say that almost 90 % of the time in Boxee, the video playback is choppy, or jumps a couple of frames every 3-4 seconds, or something is off with the audio sync..
As far as I can see on the forums, the inbuilt media player works just fine for a lot of people, but I'm not that lucky.
I really love everything else about Boxee, but since the inbuilt media player has this much trouble, how about adding support for other known and working alternatives?