If you searched for me online, you might not find a clear home for me. You would find my Facebook profile, my personal site, my MySpace profile, and more. The point is that there is a lot of duplication out there.
Technologies like OpenID are going some way toward being able to log in to multiple sites without constantly needing to make new accounts. This is good for several reasons. It is most definitely more convenient. It is also more secure because you can use an OpenID provider that support multiple factors of authentication instead of relying on every website to do so. You are also more likely to protect those authentication credentials and change them on occasion where applicable.
Another piece of the puzzle that I do not yet see being solved satisfactorily is profile duplication and synchronization. I have a Fakebook profile. I have a MySpace profile. Shouldn’t they contain the same information? I have way more than these too. Just look at my DandyId list, and that’s not even all. I want to see a solution to that problem.