Kevin Marks reports:

I made an initial conversion to hAtom by hand in the meantime, but a few weeks back Michał Cierniak and I checked in a change to the underlying Blogger templates to make hAtom the default, which the Blogger team graciously accepted. This should enable much simpler client-side parsing of the blog pages.

Kevin has more details on how to add this to your template if you're using new-style Blogger templates. Here's a note I sent to the Blogger mailing list when someone raised the "what good is it" question:

Just to clarify, hAtom was never intended to be a "syndication format"
nor to compete with Atom or RSS. It's simply designed to describe the
microcontent on webpages, such as blog posts. We used Atom because it
provides a well-defined nomenclature for describing such elements.

What can you do with it? You could provide search results that narrow
into the exact content on a page, rather that keywords that were found
elsewhere on a page. You can write tools, such as entry pretty
printers, or "reblogging" tools for quoting posts that work
universally across hAtom blogs, rather than depending on the author/
publisher to provider this for you. Because it effectively
standardizes CSS elements for blog posts, you can write CSS that works
across all hAtom conforming blogs. You can combine with other
microformats or "POSH" HTML to associate data displayed on a page
(say, the geographic location of where a post was made) with the exact
post it belongs to.

In and off themselves not earth shattering perhaps, but not bad for
standardizing a half-dozen or so tags with minimal effort for
publishers.

All templates in the BlogMatrix Platform are hAtom compliant.