There are only 6 differences between the two cameras.
1. The HV30 adds 30p to the list of available frame rates (24p and 60i).
2. The zoom rocker toggle is larger than the one on the HV20, and different.
3. The LCD screen is brighter with a better viewing angle than the HV20.
4. The HV30 will fully charge the high-capacity battery in one cycle.
5. The Advanced Accessory Shoe cover is tethered to the camera.
6. The body color is black; the HV20 was silver.
For $800, I would pick up the HV30 with hesitation, mainly because of the better zoom toggle (HV20's was a pain in the ass) and the 30P. If you want me to explain progressive I shall, but to keep it simple, it's better for sport.