Wondering if anyone else has experienced this. If I'm downloading something with Transmission (which is saving to the USB drive) then network access to that USB drive is severely hampered. I don't have any benchmarks yet but I can tell you that Windows 7 Media Center can take 15-30 seconds just to step into another subdirectory of videos. When nothing is active in Transmission, it just takes a second or less.
I should mention that this occurs even if the torrent has very little activity (i.e. downloading slowly) so it's not like bandwidth is an issue or that the drive itself is overwhelmed.