Hopefully with Google's OpenSocial API launching Thursday, I'll finally be able to tell Flickr, "Just let anyone that is my friend on Facebook, or in my GMail address book, to view my photos."
I'm tired of telling people, "Sure, you can view my photos. Just create an account at Yahoo, then login to Flickr, then let me know your username." I already know these people somehow, and that relationship is somewhere on the web (probably in my address book) so why can't I tell Flickr to use that?
The idea of a portable set of relationships which enable cross site permissions is really, really important to the scalability of the web. Our data is spread out, it's in a web. Let's use it on the web!