I was just looking at the D3s' video specs and other than the iso range it seems to be similar to the D300s. One thing I was wondering was that can you record for longer than the D300s' 5 mins at full res and 24fps. This would make a big difference I would think.
One difference of course is the sensor size that should open more doors for creative limited DoF shooting,
Besides, potentially lower noise that could enable the output to fare better when being extrapolated to full HD displays. This would have to be confirmed with actual tests.