I use a GoPro Hero 3 Black Edition as a fourth camera for video shoots.
You can shoot at 60fps at 1080 and it amazes me how much footage you will get on a Class 10 (has to be C10 if using ProTune) 32G Micro SD card. I use SanDisk Mobile Ultra UHS-I Micro SD SDHC 32GB which are insanely cheap.
In this, the drummer is being shot with the GoPro (1080P @ 25FPS). Admittedly I have done a lot of noise reduction in post, but this was a stupidly dark gig. http://youtu.be/rPvIGg5Q7P0?t=20s
Slowmo at 720p @ 120FPS is excellent but WVGA @240FPS is only worthwhile with great light and the right source material.
Bloody great fun either way.