Here is a video that talks about some more advanced usage of the quaternion double-cover property, and specifically how you can use this to eliminate unwanted blending problems in your animation system.

One thing to note, is that I get a little too excited in one part when I'm doing a physical demonstration of a blending glitch, and I accidentally say "extra 720 degrees" instead of "extra 360 degrees". There is never an "extra" 720 degrees so while most of the time I say "extra 360" in the video, I do slip up once so please don't let that throw you :)

Also, Dave Moore from RAD Game Tools sent me a link to this cool web page that shows how to do the belt trick I mentioned in the lecture: http://gregegan.customer.netspace.net.au/APPLETS/21/21.html.