I installed the following driver update.
http://www.viaarena.com/default.aspx...0&SubCatID=122
Even though my 2 DD4's were working properly, I thought I'd try this update. It has slashed my channel change time considerably. Also if I select live TV from the guide I no longer see a wait symbol - it goes straight to TV and a moment later the picture appears.
This driver update is supposed to improve compatability for the VT6212 chip (used on the DD4) so may resolve stability issues some people are having.
Good luck.