My primary DSLR is a Canon 5D MKII, with an older Canon 450D as a backup body that I use mostly for a set-and-forget timelapse unit with a cheap intervalometer. I've recently moved to using a GoPro HD Hero 960 & GoPro HD Hero 1080p for the TL's I would use the 450D on, although there are very severe limitations. I've got an order in for the new HD Hero 2, but stock levels in Australia are limited so it's about a week away.
The first challenge for a serious photographer with the GoPro is the limit of two metering modes; the default center weighted average and spot. The former for most general uses, and the latter to meter from the center point, similar to what you will be familiar with spot metering off your center AF point. This is useful when shooting from inside a car, and we use this mode while rock climbing, where the metering would range wildly from sunlight on a cliff, and the darkness of a crack/arête.
This is about all you can control, with the unit handling the white balance, tonality and exposure itself. The lens is technically an f/2.8, but it doesn't exhibit the DOF you would expect from such a wide aperture due to FOV and the automated control. Check your metadata when doing test shots in varying conditions to watch those values ramp. The GoPro angle is that "everything is in focus", but in reality this is dependent on the conditions. We're not talking about F22 on a tripod, and the closer the objects are, the better. The metering and exposure favour timelapses as the slower shutter speeds give the "shutter lag" that you want in a good dynamic timelapse video. Slower shutter speeds = drawn out motion, which animates smoothly (rather than a series or crisp images which become jerky when compiled).
The camera shoots at 5MP regardless of video settings, so we're talking about 2592 x 1944 pixels. This makes it fiddly when using timelapses with video shots, but even with a 1080p shoot you've got plenty of room to scan within those absolute dimensions. In other words, the photos are "bigger" than the video, so you can actually do post-production "pans" across the the compiled timelapses. You can mock short dolly or crane movements. Worth the hassle.
I have no idea what the 11MP of the new GoPro will be like, and I'm a little nervous thinking about that tiny sensor packing more receptors on it. Early reports seem to be "good".
So in comparison? There is no comparison. Photo quality will vary like you would expect on a Canon IXUS. You can select between two metering modes, and you can move the camera around. That's it. Some bright scenes will be overexposed, and the pre-HD Hero 2 cameras perform relatively poorly in low light - especially for digital noise. Focus is an issue, due to the FOV and wide-angle, with the usual colour skew at the edges of the wide-angle. Claims of an f/2.8 lens should be ignored, as they raise confusion questions about DOF that doesn't apply. Pretend it's f/11 and treat it as you would a kit lens at that aperture. It's a tiny, cheap, CMOS sensor, but it is packaged so cleverly that it suits its market well. And I love it :)