My experience has been different than the rest of you. I bought a GOPro Hero 3 Silver edition last September and used it about 8 times. I bought it on a closeout at Best Buy because the 3+ was due out. We Here is my personal review.
The early Hero 3 had some serious software issues. If you go to the GoPro website and do a search, you will find an apology from the CEO. They revised the software to fix the freezing issues etc.
We are ATVers and I mounted the camera to my helmet.
The good: Excellent picture quality in various lighting conditions. HD is really amazing. Captured Colorado fall colors well. Very wide angle lens. I captured some great video first time out. The camera functions and settings are easy to understand. Lots of mounting options.
The bad: Very expensive and very over packaged. Standard battery lasts less than a half hour. You have to buy the larger piggy back battery which then extends life to about 2.5 hours. If you enable the Bluetooth remote it is a serious battery hog. The battery for the remote has a very short life. The free editing software you download from GoPro is very minimal. I understand that the Hero 3+ has addressed the battery issues.
The GoPro would work as a dashcam. I would suggest using a 12V to USB adapter to power the camera and the remote. I would think you could find a cheaper alternative for what you want.