I noticed that our friends at UserVoice now support OpenID:
This means you can (finally) log into both sites (stackoverflow.com and stackoverflow.uservoice.com) using the very same OpenID. I believe they're using RPXNow to implement this feature.
Hooray for open interoperability, and open identity standards!
So I guess that's what Richard was hinting at when we interviewed him on Podcast #30.. who knew? :)