I am going to add a note of caution, however. Talk is cheap. Joining the OpenID Foundation means very little by itself. It’s what these companies do next that is important. For instance will Google enable users to authenticate to Gmail from another OpenID identity provider? Will Yahoo! or Microsoft? Or will these companies only support being an identity provider.
I expect the later, although I would love to be proven wrong. Right now there are many OpenID providers and a dearth of important relying parties and that is preventing OpenID from being really useful.