I have had a hard time finding decent overviews on OpenID, the specs are there (and they aren't too bad) but they are hardly a quick read. The linked presentation goes someway to addressing this.

BTW: The whole presentation is implemented in a single HTML page, controlled by CSS. Neat.

A good site for treatments on how to make your presentations more successful. Look out for the "popular posts" linked on the right - there are some good ones in there.