So I ran the test... The failures were so minuscule, its unlikely anyone would run into problems with a site because of it. And since HTML5 is nowhere near a standard yet, it matters even less.
If IE9 can pass the Acid3 test with 100% and go through the passes instantaneously, then I would be impressed.
Heres what I found that failed (Chrome 7.0.514.44 Stable):
- A canvas element abstraction wasn't recognized (big whoop).
- A div border (relative in size to its parent element) that was too small. (could make a site look a little strange, assuming you want a ~200px border on a div).
- A couple were HTML5 video parameters that weren't recognized, but nothing that would prevent videos from actually playing.
- The only other one of note was a CSS3 pointer that was applied while inside an HTML comment tag. I can see why this is the case because I have no doubt that many developers are still wrapping thier CSS with <!-- and -->. Jussayin