
Blogger inserts this line in the head section of your template:
<link rel="openid.server" href="http://draft.blogger.com/openid-server.g" />
so now you can use any of your blogs as an OpenID. Some simple things you can do with your OpenID are to claim your blog at Technorati (you still need a Technorati account), sign in using your OpenID at Plaxo, Zoomr or post comments in a LiveJournal blog, like Brad Fitzpatrick's blog. A small inconvenience is that Blogger uses the subdomain of your blog instead of your name.
Yesterday, Yahoo announced it will support OpenID 2.0 (Blogger is a provider for OpenID 1.1), so the future is bright for this authentication system.