It isn’t hard to notice how HTML5 and WAI-ARIA seem to conflict each other. They often provide elements and attributes that seem to do the same thing. In some cases, outright conflict each other (for example, WAI-ARIO requires one h1 element, but HTML5 allows multiple h1 elements nested in sectioning elements.
The W3C seems to be taking some steps to clarify how to use both together in Using WAI-ARIO in HTML. As of June 13, 2013, it still in draft, but it provides a lot of insight. I already have more work to do to fix some issues with this site.