Group membership and OpenID
Martin Atkins has posted a note about the Group Membership Protocol to the OpenID mailing list.
[the] Group Membership Protocol is a very simple means by which a group of URIs (which are probably OpenID identifiers, but don't necessarily need to be) can be enumerated and queried.
This looks very interesting. A simple idea but one that appears to have lots of applications - many of which will lie outside the identity management area, possibly including those that currently fall under the 'collection description' umbrella. It'll be interesting how it develops.