This guy has some other really great articles if you search around his blog a bit. Here's few I have bookmarked.

http://www.wildbunny.co.uk/blog/2011/04/06/physics-engines-f...

http://www.wildbunny.co.uk/blog/2011/04/20/collision-detecti...

http://www.wildbunny.co.uk/blog/2011/03/25/speculative-conta...