We've just enabled OpenID signed comments for Blogger in Draft. There are a few rough edges still (which is why you have to enable it for your blog by going to draft.blogger.com), so we're looking for feedback. We're also working on enabling Blogger as an OpenID Provider, meaning that you can use your blog URL to identify yourself on other services.
What's particularly fun about this is that it's been a very collaborative project, bringing together Blogger engineers, 20% time from a couple of non-Blogger engineers, and last but not least some of the fine open source libraries provided by the OpenID community. Thanks all!