Well I got it up and running and after a couple of updates it looks pretty good and works well so far. I'm only going to using this for streaming content off my PC so I don't really care about any of the apps like Netflix, which I haven't noticed on the box yet. I think it's found all my stuff and categorized everything correctly.
I can only compare it to other devices I've used for streaming; PS3 with PS3 Media Server & TVersity and the original XBOX running XBMC. So far I like the Boxee more in just about every aspect. Nice video wall, full MKV support, fast forwarding and rewinding works well, subtitles and other audio channels can be controlled with the remote, etc...
Navigating through the menu is a little laggy but I'm used to PS3's snappy navigation. Haven't found anything it can't play yet, although one "HD" DviX file didn't seem to play so smoothly. I'll have to keep going through more stuff.
I'll update if anything new comes up.