It did not properly work in my system's USB 1.1 slots. It was unable to tune any channels and eventually caused my system to lock while doing the dvbscan for ATSC channels. Luckily unplugging it unlocked the system.
After plugging it into a USB 2.0 card on the same system, I successfully ran the dvbscan with no trouble.
I just (April 2nd 2010) purchased a WinTV-HVR-850 model 1200 through amazon.com, and it appears to be a different version then the two listed. This one has a serial number of B1F5 and is not detected by Ubuntu Karmic or Lucid beta. I have yet to be able to get this model to work!