Does anybody use Go Pro for their time lapse videos? I am especially interested in feedback on the Go Pro Hero 3 Black, but any Go Pro feedback would be helpful. I'm thinking of trading in my Pentax Optio for a Go Pro. Thanks!

I've done a few with an HD2. Haven't done any with my Hero3 yet. You can see a few of them here

I have been using my Hero3 Black for a couple of timelapses now. It works very well and I am very surprised how smooth the camera adapts to lighting changes over the timelapse period. It nearly doesn't induce any flicker even at a sunset when light changes fast.
The image is very sharp. You always have to remember it's a Action Cam. It just records pictures in JPG so tweaking the picture in Post isn't as comfortable as working with RAW files. Also low-light capability isn't comparable to DSLRs even if it performs quite well. Another key feature is the extreme wide angle lens so that gives you a special "GoPro-Look". The battery of the Hero3 is the weakest thing of the camera. For timelapse it lasts not more than 1:30h. I tried a timelapse of the snow at around -5°C and the camera shut down after just 30minutes. So Battery life is depending on it's temperature.
So in my opinion it isn't a camera I would use for all of my timelapse work. It's a very nice addition to a DSLR to get some shots you could achieve with a DSLR or to shoot nice BTS.

here is one i did with my hero 3 black

https://vimeo.com/61042337

I used a GoPro HD Hero 2 exclusively for quite a few videos and as a second for the remainder. The portability and wide-angle are excellent but there tend to be three rules of the Hero 2 (and to a lesser extent the 3): light, light, and light.

The optics aren't fantastic but the portability can't be beat. I use it as a BTS camera a fair bit. I even attached a big magnet to a mount so that I can attach it to (get this) a drywall screw embedded in a wall among other things. I've mounted it to the hood of cars, small and RC aircraft, and a high-altitude recon balloon.

You should have one in your kit. They're too much fun not to have.