A 4mn clip comes to 360MB in H264 video from the camera, and I can recompress it with virtually no visible loss of quality to 100MB with mencoder set at 3200kbps for H264 (or almost 100MB/mn down to 25MB/mn).
Changes with the GoPro HD so far are:
Here are some pictures comparing GoPro HD colors vs GoPro Wide (that's the 2 pictures per second mode where both GoPro Wide and GoPro HD take 5Mpix pictures). Just in case you ask, pictures were taken just a few minutes apart with the same amount of sun.
GoPro HD: Nice crip picture, somewhat dull colors
GoPro HD: Still nice crip picture, somewhat dull colors
GoPro Wide: Picture slightly less crisp, more vivid colors, more blurry around corners
GoPro Wide: Just prettier picture except for blurriness around corners
So far, I'm a bit torn, the every 2 second pictures are just nicer on the older GoPro Wide for me, and the early bugs on the GoPro HD had better get fixed (SDHC support and taking pictures upside down at least). No idea if the washed out colors problem is solvable or not. If not, that would be a shame.
But yes, the full 1080p HD video does beat the old 512x384 videos hands down though :)
Here is a link to the full 1080p video recompressed to 3200kbps and a link to the youtube page with the video (which allows 720p and 1080p viewing).