Just out of interest I tested Nvidia NDPAU patch, which offers hardware decoding of h264 and mpeg2 streams. Here is a short howto and a testing video:

http://www.kdenlive.org/kdenlive-nvidia-vdpau-ffmpeg-patch

Dang, I'd like to see this.

Oh and ATI's XVba/XVmc while we're at it. (OK, once they've given specs / patches)

Yes, FFmpeg snapshot of 2008-12-17 includes xvmc support. But it is only for mpeg2 decoding, whereas Nvidia VDPAU covers mpeg2 and h264 (AVCHD). Nvidia solution seems to cover all video editing needs.