I absolutely love my Boxee. I have a Slingbox on a TV in another state, so I can watch the sports feed from that state easily on my TV with the Boxee Slingplayer app. Very good solution for long distance sports fans or sports fans who travel.. with NO monthly fees for Boxee or Slingbox!
With a Boxee, add Fuzzthed's third party repository (google for easy instructions on installing 3rd party repositories to Boxee), for access to content Roku can't provide.
I also have a Roku and never watch it due to to Boxee's Slingplayer app and Fuzzthed's options.
I also love having the Boxee "watch later" tab on my computer to sync videos from the internet for viewing on my TV. I do this often with youtube free movies or funny video clips.
As for my own media collection, Boxee plays the most file formats, which was an important factor for me.
from Boxee FAQ's page
18. Which video formats can Boxee play?
Boxee supports Adobe Flash 10.1, FLV/On2 VP6 (FLV/FV4/M4V), H.264 AVC (TS/AVI/MKV/MOV/M2TS/MP4), VC-1 (TS/AVI/MKV/WMV), MPEG-1 (DAT/MPG/MPEG), MPEG-2 (MPG/MPEG/VOB/TS/TP/ISO/IFO), MPEG-4 (MP4/AVI/MOV), DivX 3/4/5/6 (AVI/MKV), Xvid (AVI/MKV), and WMV9 (WMV/ASF/DVR-MS).
19. Which audio formats can Boxee play?
Boxee supports MP3, WAV/PCM/LPCM, WMA, AIF/AIFF, AC3/AAC, OGG, FLAC, DTS, and Dolby Digital/Dolby True HD
20. Which image formats can Boxee display?
Boxee supports JPEG, PNG, GIF, BMP, TIFF.