Yesterday, in addition to launching Blogger in three new languages, we pushed out a draft feature: Your blog is your OpenID. Technically, this means that Blogger is both an OP and an RP; we've accepted OpenID signed comments since December.
We've implemented OpenID 1.1 so far, so we should be compatible with all OpenID 1.1 RPs. Please test it out (see instructions for opting in) and let us know if you see problems.
It's also great to see Yahoo announcing that they'll be an OpenID 2.0 Provider. I hope they implement RP support soon too, at least for things like Flickr comments.