I have the LT-H90LAN, it can play most DivX and XviD files I have and for youtube videos, I download them as mp4 and I can play them back on the player, I did not notice any slow playback problem using the USB drive make sure you have latest firmware installed.
There are occasional problem with some videos as with any hardware player. It should also be able to plaback mkv files, I did not try it yet.
I wish Buffalo would have put two USB ports in the backbe cause my HDD cannot draw enough power from one that would have more neat than the one in the front.
Also the power button on the front just put the device in standby, something you can do from the remote, to power it off completly you have to unplug it.
Message Edited by pb200805 on 01-16-2009 04:22 AM