W3C HTML Accessibility Task Force
As a number of people have stated, there are some accessibility issues in HTML 5. Hopefully the HTML Accessibility Task Force will help straighten those out:
The objective of HTML Accessibility Task Force is to help ensure that HTML 5 provides features to enable Web content to be accessible to people with disabilities. This includes review of existing features for potential accessibility problems, and proposal of new features where needed.
Material related to accessibility in HTML 5 can currently be found at the HTML ESW wiki, the PF (Protocols and Formats) ESW wiki, and the PF wiki.