I upgraded to iOS 4.3 last night on the ATV2. I use an iomega iconnect to allow XBMC to connect to my media on a western digital USB via samba share over the network. I have many of my movies in .MKV format so I can get full Dolby 5.1 when watching them on the ATV.
In the previous version of XBMC (from iOS 4.2.1 untethered boot), I was able to play MKV moview. In the new version, accessing .MKV files causes XBMC to crash and I'm returned to the main ATV home screen. MPG and AVI (and MP3) play fine in XBMC.
Is this a known issue with XBMC? Is there anything I can do to troubleshoot it more?