I recently bought the GoPro HD to replace my GoPro wide. The rationale was of course to get HD video, and for that the GoPro HD does deliver (full 1080p 30fps video).
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:
it's just very slightly bigger and heavier, but my plane still takes off with it
it has an internal li-ion battery which should last a few hours (GoPro Wide lasts almost 2H for a set of rechargeable AAA batteries).
the current firmware does not support shooting upside down, which I do in my plane and car. For now, I use software to flip the images and video.
more importantly, it's supposed to support SDHC up to 32GB, but for me it fails with my 16GB card so I use 2GB SD for now (that's only about 20mn at full quality before it fills up though). Hopefully they'll fix it in a new firmware.
more sadly, colors look washed out on the GoPro HD for me. I contacted support about this and will see what they say.
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).