New features in HTML5 mean new accessibility issues, whether problematic or no (there's some disagreement on this). Here are two resources for keeping up with the current status quo:

• html5accessibility.com includes tables detailing each browser's HTML5 accessibility support, with numerical rankings alongside more qualitative notes. The site hasn't been updated since July, which will become more of an issue as more rapid-releases (especially Firefox) appear; but for now, at least, the site has a lot of great info. Also includes tips for accessibility support workarounds.
  
• Steve Faulkner's 'HTML5 canvas accessibility discussions 2009-2011' page organizes and reformats Charles Pritchard's in-depth review of three years in HTML5 accessibility discussions, an overview of relevant conversations on the public-canvas-api email list. The back-and-forth hyperlinked emails, which in many places conclude in aporia, reveal a bit more about the deeper disagreements still plaguing the development of HTML5 accessibility.

The SVG vs. Canvas debate touches closely on the accessibility issue -- so even if you're not terribly fascinated by accessibility in general, anyone interested in interactive web graphics should find these two pages interesting.