I've used a GoPro HD Hero (the one before the Hero 2) pretty extensively and use it almost exclusively at the "narrow" FOV setting and 1080p, and it works brilliantly well for helmet cam footage when mountain biking and it spent a brief time clamped to the roll bar of my Miata during autocross runs and some backroads runs.
Here's an example of helmet cam footage I shot on the HD Hero this past October at Bryce Bike Park (that was me riding and doing the HORRIBLE 2-stroke impression, btw!) and here's an autocross run with the camera on the roll bar in the Miata, with the lens on the housing scratched from a fall the camera took a few months prior (suction cup mount + bare primer...)
I definitely like the camera and have been using it for over 3 years without any issues, and will continue to strap/stick/bolt it to whatever I can, but it has its limitations. I'm not a terribly big fan of the mounts, each one only has 2 degrees of freedom (the little dogbone mounts have one end 90 degrees out from the other), the sticky mounts do stay put VERY well (3M VHB is some seriously good adhesive) but the bases that slide into them occasionally have some play that's kinda difficult to get rid of. If you need to tether the camera (a must for racing I think) there's not really anywhere on the waterproof housing itself to tether to without drilling holes or using the surfboard mount's stick-on tether. Also, it's got all the aerodynamic appeal of a Jeep XJ Cherokee with rally lights and a roof rack, although for autocross that isn't much of an issue. There's the FOV deal, the HD Hero and Hero2 both have barrel distortion, and the Hero3 and 3+ have it as well, but it isn't as pronounced. I shoot in 1080p 30fps 135deg FOV, which is the narrowest angle the HD Hero or the Hero2 can manage, although the Hero3 can go slightly narrower I believe, and the image quality of the Hero3 black edition is phenomenal. Unless you get an AIM datalogger with a GoPro cable, I don't think there's any way to overlay telemetry onto the video, but I could be wrong about that. If you have to plug any cables into the camera while recording (external power or mic, for instance, or a HDMI-out) you need the skeleton housing, which is definitely not waterproof, and the camera itself is not designed to be water-resistant, although a few raindrops won't hurt it.
This christmas I'm getting a Replay XD1080, which I think will work a lot better for in-car recording. It has an optional cable that replaces the rear cap and plugs into a cigarette lighter (or the cigarette lighter plug can be cut off and the cable hardwired to a 12-24v source, how they deal with that much voltage variation I have absolutely no idea but for a car you won't have much more than 12v to play with anyway) that also has a 3.5mm external mic port, so you can mount the camera out in the airflow without having the same soundtrack as a Cat5 tornado, all while keeping the camera itself water-resistant (both the front cap/lens bevel and the rear cap are O-ring sealed). the aluminum mounts for the camera that RePlay sells are stupid expensive, but do allow you to mount the camera to anything from a 1913 Picatinny rail on a pistol/rifle/shotgun to the trucks on a skateboard to a car's rollbar, depending which mount you buy (buying all of them would set you back at least as much as the camera itself), although the "standard" plastic mounts are fairly reasonably priced so mounting to a mostly flat surface shouldn't be an issue, as long as it's more or less parallel to the direction you want the camera facing. Performance wise, the XD1080 (and its little brother, the XD720) has a maximum FOV of 135deg, with none of the barrel distortion of the GoPro, and when shooting in 1080p the FOV drops down to 110deg. The GoPro Hero3 Black Edition DEFINITELY has the RePlay beat in terms of image quality, with a 15MP sensor and up to 4K Cinema video resolution, as opposed to a 5MP sensor and up to 1080p resolution for the XD1080 and 720p for the XD720, but both models of the RePlay have better low-light performance. The RePlay's advanced settings can only be adjusted via editing the text file on the memory card, but you do have more control over the camera settings than a GoPro gives you, even with the iPhone app. If you so choose, you can get a HDMI-out cable for the RePlay and stream to a recording box (or a datalogger with HDMI-in capability, although you can't control the camera with the datalogger like you can with an AIM/GoPro combo) or a transmitter, if you want someone in the pits/on the sidelines to be able to watch your AX run in real-time. The built-in mic on the RePlay is great as long as there's no wind, but it is VERY sensitive to wind and a light breeze will end up sounding like gale force winds, unless you use a little sticker over the mic port, which only helps marginally. RePlay does sell a hardwired remote designed specifically for using the camera in a race car, is designed to mount to a bulkhead/sheetmetal dashboard, and can turn the camera on/off, start or stop recording, as well as serve as an external power source, HDMI-out cable, and 3.5mm external mic adaptor, but it's VERY spendy at $100 for the cable itself.
The RePlay XD1080 is essentially a GoPro Hero3 White Edition (HD Hero guts, but in the smaller/lighter form factor of the Hero3) with better low-light capabilities, an easier-to-use/more aerodynamic form factor for automotive/racing usage or strapping to the top/sides of a helmet, less internal battery life (hence all the ways RePlay provides to extend said battery life, like external battery packs and hardwire adaptors to a 12-24v source), a woefully bad internal mic (a non-issue if running one of the power cables with a 3.5mm mic jack), but for $50 more. For an automotive/racing application, I think it's worth it, but YMMV