I've been eyeballing a GoPro for a dash cam since it also overlaps with my other hobbies (cycling and ATV riding). The big drawbacks seem to be the low-light filming and the fact that it doesn't automatically turn on or automatically rewrite when the disk gets full.

The GoPro 3 Black low light performance is quite good (much better than earlier versions).

Yeah, plus it's much more tempting to thieves or kids who want a GoPro.