I have a little collection of Hero 2's. They do quite well, depending on what you want to record. I use mine for recording when I go flying.
The Hero3 Black Edition is a much better camera, only depending on if you are using it in low light, or in burst mode. It also records at 1080p60. The Hero2 is only 1080p30. It has the wifi built in (you have to add it with a Hero2). The flat lens also films better underwater (add a red filter, colors are better). On the Hero2, this is an accessory.
The White edition is a good little camera for just recording video. $200, you could buy 2 for the price of the Black edition.
The Silver edition is about the same as a Hero2 (1080p30, 11MP/10fps burst, wifi built in). The White is less (1080p30, 5MP/3fps burst, wifi built in). I usually just buy the best, so I will compare the Black edition.
So..........
Hero3 (Black)
1080p60
12MP
Wifi Built in
12MP 30fps Burst
flat lens
3D not avail yet
Hero2
1080p30
11MP
Wifi is an accessory
11MP 10fps burst
Flat lens is an accessory
3D accessory
I will be keeping 2 of my Hero2's because I have the 3D kit, but will upgrade to one or 2 Hero3's. Mainly for the low light aspect and burst mode.