Boxee over wired gigabit ethernet buffers when playing back the following video file:

General
Format : Windows Media
File size : 116 MiB
Duration : 7mn 29s
Overall bit rate : 2 156 Kbps
Maximum Overall bit rate : 128 Kbps
Encoded date : UTC 1970-01-01 00:00:00.000

Video
ID : 1
Format : WMV2
Codec ID : WMV2
Codec ID/Info : Windows Media Video 8
Description of the codec : wmv2
Duration : 7mn 29s
Bit rate : 1 934 Kbps
Width : 960 pixels
Height : 528 pixels
Display aspect ratio : 16:9
Frame rate : 29.970 fps
Bit depth : 8 bits
Bits/(Pixel*Frame) : 0.127
Stream size : 104 MiB (90%)

Audio
ID : 2
Format : WMA
Format version : Version 2
Codec ID : 161
Codec ID/Info : Windows Media Audio
Description of the codec : Windows Media Audio V8
Duration : 7mn 29s
Bit rate : 128 Kbps
Channel(s) : 2 channels
Sampling rate : 44.1 KHz
Bit depth : 16 bits
Stream size : 6.86 MiB (6%)

Using the Info option, CPU load shows 100% on Boxee Box. Plays back ok for the first 30 seconds, then audio disappears and playback buffers continually. Playback does not recover from 100% CPU load.

File plays back with no problems over wireless network to Win 7 PC and Windows Media Player.

Edit:
Boxee using latest firmware.