I'm using the nvidia driver on Debian testing AMD64 with out any problems (except that I had to install a newer kernel when installing the driver).
When comparing to the open-sourced driver I've also noticed that the nvidia is faster than the nv (at least in my case).
To be honest I've chosen the nvidia driver because I sometimes play the 3D games;) But as for watching the movies - it is possible to use OpenGL as a video rendering driver (for example one can set it in xine or in mplayer) instead of the Xv (X-video) driver. I haven't noticed any difference in xine but in mplayer the GL driver worked better than the Xv (don't know why). Of course when using the OpenGL for video playback you need the hardware 3D acceleration (the nvidia driver).
I think it's worth trying out both drivers and seeing which one is better for you (installation of the nvidia driver is not as hard as it may seem at the beginning;)