I am streaming content from a HD connected to an airport extreme (a 720p mkv) and the video constantly buffers. It is inconsistent happening every 5-8 minutes. I have never had streaming problems in the past until the most recent update. Over the last weekend, I updated my atv2 with the most recent redsn0w jailbreak and most recent AVT Flash Black OS (2.0.2).
Netflix streams HD just fine and if I run the video from airplay mirroring (off my macbook air), things are fine as well. My only conclusion is to assume something is up with the way the new software buffers. I rebooted the ATV via the Maintenance/Settings menu but to no avail.