Open ID Commenting is available on all Blogger blogs if you have "Anyone" or "Registered Users" allowed in your comment settings. In the comments, an icon will appear indicating whether someone is commenting via Open ID. There's a little Blogger B showing now for folks who comment via a Blogger account name.
One cool bit is that if you use Open ID, you can designate what site you're linking to. In the Blogger Buzz post, here's an explanation of the code you can add to a personal site to delegate your Open ID link go there. This article on Intertwingly explains more about Open ID delegation. I have no reason to try it, but it sounds pretty cool and a way for people to leave links in comments to their sites. There have been complaints that Blogger no longer allows people not on Blogger to leave links. Other commenting services like Haloscan and other blogging platforms with built-in comments usually have fields for you to type in your "name," "email," and URL. Open ID, however, does this automatically, and a lot of services are on Open ID these days. To demonstrate, I'll comment on my own post, using my LiveJournal Open ID.