This demonstration works in Firefox 3.1 beta 3 (well, at least linux, I didn't have time to test with others). A bit more work could be done to make it work with webkit. To see the east asian Ruby annotations, you'll need the XHTML Ruby support extensions. If you wonder about the layout, check the building where the demo was done.
HTML Video
with DFXP captions
Ruby annotations:
これは
MathML:
Shiny effect using CSS!
Several Web technologies in ONE document