Will a gopro make a good dashcam?

I'm thinking of buying one as a dedicated dashcam. I know there are products made specifically for this purpose but Gopros quality seems hard to beat. Since this would be a permanently attached camera I need it to do a few things, which I'm not sure it is capable of doing.

1) can I power it through the cigarette lighter for constant power?
2) is there a loop mode in recording so it will override old footage and record non stop? Or can i format the memory card easily?

Basically, I'd like to mount it and forget about it. Only if something happens, then I would dismount and download.

Or better yet, I'd like to use my iphone as a recorder with an external camera. I see that the ContourGPS camera has an app where you can use your iphone as a viewfinder, but you can't record the image using the phone itself. That would have been perfect, if it could do that.

The image quality is gonna be better than most, but unfortunately the loop thing isn't an option. Constant power can be done, via USB.

I use this any time I operate any vehicle:

KCI Smart Black Box. It records 640x420 video continuously whenever it has power, and it will also track your coordinates, speed, and g-forces if you want it to. It does not record audio. It also has a capacitor so it'll keep running for a few extra seconds even if power is cut.

I love it - I have mounts and wiring set up on all my bikes so all I have to do is plug the camera in and go. I also have a Contour GPS but only use it on the bicycle.

^ cool.

you can also couple a camera which offers live feed to a recording box in your vehicle.