I guess what is supposed to be most striking is the horizontal slide show at [EDIT: that did not originally show for me in Safari 4.0.5]:

http://apirocks.com/html5/html5.html

Which didn't seem remarkable till around slide #31:

http://apirocks.com/html5/html5.html#slide31

- whose css-controlled number of columns ( -webkit-column-count: 3; ) I had never seen before.

EDIT: For real usability a TOC of the numerous slides + info on cross-browser testing would have added huge value.