No original research, just a collection of links. These all link directly to the lensrentals blog (I have no affiliation with them), and are specifically interesting to Canon shooteres. The lensrentals blog is one of the best in photography of which I have knowledge.
http://www.lensrentals.com/blog/2010/07/how-autofocus-often-works
http://www.lensrentals.com/blog/2012/07/autofocus-reality-part-1-center-point-single-shot-accuracy
http://www.lensrentals.com/blog/2012/07/autofocus-reality-part-ii-1-vs-2-and-old-vs-new
http://www.lensrentals.com/blog/2012/07/autofocus-reality-part-3a-canon-lenses
http://www.lensrentals.com/blog/2012/08/autofocus-reality-part-3b-canon-cameras