Most of the apps that have been produced as a result of this are TOTALLY RAD.
One of the newest ones, written by ciro@tokyo, displays a graphical representation of the semantic network of a Flickr user's tags. This is a picture of my tags, and it's an uncanny representation of my life over the last year or so. (Although it's not uncanny at all really, because I lived it, photographed it, and then organised the pictures.)
As the entire universe is wondering about how the usefulness of this tagging schwag can be defined - you know you are - we often run into the hurdle of what to do with the unstated connection between similar words. Even though this is a map of my actual tags (and my life!!), it would be really interesting to blend that data with a thesaurus or something.
I also wonder what would happen to this sort of representation if the words were replaced with photos. Would we be able to navigate that? Would it make sense?
It's such a blast to see the API in the hands of some unfettered left-brain types. More!