A neat feature of the OpenID technology is that it allows you, the developer, to verify that the user indeed has ownership of a URL endpoint. I had stated earlier that lifestreaming services are going to find this feature very useful. Services like FriendFeed, Plaxo Pulse (and of course, MyBlogLog) can enable users to verify ownership of their various online identities/profiles, thereby promoting more authentic activity feeds and eliminating the impersonation scenarios that will inevitably come up.
More generally, once a user has proved to your service that he owns a particular URL endpoint using OpenID, interesting things can follow. Your service could retrieve (you should do this under user consent and control, of course) user attributes that lie at the verified URL endpoint. The retrieval is significantly easier if the attributes are marked up with the appropriate microformats. I am sure people will come up with many interesting features by combining this simple, yet powerful, capability with technologies like YADIS, FOAF/XFN, MicroID.
Now, for the big news of the day. Today, we rolled out support for MyBlogLog profile URLs as OpenID identifiers (Ian Kennedy's post on the MyBlogLog blog). With this change, we have also eliminated the only-one-custom-OpenID-identifier per-account restriction. This means that you can select both your Flickr photostream AND your MyBlogLog profile URL as your OpenID identifiers, in addition to creating a pretty me.yahoo.com identifier. Simon, we heard you loud and clear. :-) This change is especially exciting because the folks at MyBlogLog have been awesome about implementing support for hcard, XFN, FOAF, in addition to hosting a pretty rich profile complete with the New With Me activity streams feature. We hope that you will find this change useful and that it can act as an enabler for more fun applications of the OpenID technology in the future.
To set your MyBlogLog profile URL as your OpenID identifier, start here (requires logged-in state).