I love my Hero3. The only thing I don't like is how it proves that the stuff I do really doesn't look as cool as I thought it did...
I use mine for skiing and fly fishing. When I'm skiing I use 720p 60fps mounted on a chest harness. I used to wear it on my helmet but I don't like the angle on the snow, especially when the lighting is bad. The chest harness gives a little better perspective and its easier to mess around with the camera when I'm on the lift instead of taking off my helmet ever time. When I fly fish I use 1080 mounted to an old chopped up ski pole that I attach to my backpack or float tube. I'v capture some pretty cool fish footage when I'm stringing them in. I haven't had any battery life problems as long as I keep the wifi off and I haven't had any SD card failures yet either. I use the 32gb micro sd.