I think <hgroup> is one big step backwards for accessibility. Unless something with it will be altered, all examples I seen are:
<h1>My Cool Company</h1>
The h2 in the first block and the h3 in the second should be paragraphs not headers. It breaks what a heading does, which is give hierarchy to a page/document, in my opinion.
<h2>Blog post title</h2>
<h3>Post meta data</h3>
One thing I think hgroup could be cool for would be allow browsers to create an outline of the page. I think Opera does this already. However if you could make the outline, you would need id's to show which heading is a child to what. But wouldn't just adding a new attribute to <hx>'s be cleaner? Yes! Therefore hgroup is useless.