I recently (August 2010) purchased two additional 16GB SDHC class 6 cards from my dealer. The brand I am using is Hoodman RAW.
I have not been able to format these new cards in camera. I go thru the format process and everything appears to work but as soon as I try to record I receive this error message "Cannot Use in Video Mode" with the A or B card indicator.
My previous Hoodman 16GB cards worked great. I have just updated firmware on the camera to make sure everything is up-to-date.