On MySpace, when you need to prove that you are who you say you are, you take a photo of yourself holding a piece of paper with a certain message on it and e-mail it to MySpace.
That effectively proves that you are indeed a real live human being... but that doesn't mean you are, in fact, you. You could have set up a Charlie O'Donnell profile and put up your own pictures, then e-mailed a picture of yourself saying, "I'm Charlie O'Donnell."
I just checked out ClaimID. Its basically del.icio.us... tagging incidences of yourself with a bookmarklet and it will present them on a highly search optimized "about" page. However, I don't see what stops anyone else from claiming you. I guess that might be their model... "Claim yourself before someone else does."
My bank seems to do a pretty good job of figuring out who I am... I guess there's little chance that anyone else would know my mom's maiden name and my social security number. But I don't think I'd give either of those out to a web service.
What you really need, at minimum, so a technorati type service for claiming stuff. So, something that crawls my LinkedIn page, then tells me to change something on it within a half hour or something. That's good proof that I own that page... and then my blog... and then other services I may be on... and then they might do degrees of seperation. So, if I own my blog, and someone links to it and says, "Charlie O'Donnell is a cool guy" then they're probably talking about the same me because of the link.
Are there definitive ways of proving who you are in other creative ways?