Pretty much everyone agrees that Gravatar rocks. A global avatar that shows up wherever you make a comment on a blog (sometimes even in your desktop apps). And I don’t think anyone other than naive VC guys wants another “social networking” site, so I’m not going there. But, imagine what would happen if every time you made a comment on a blog that used Gravatars a ping was sent off to the “Gravanetric” servers with two bits of information the hash of your e-mail and the root url of the site you posted too.
Then you could start to graph shared interests. Imagine a simple force-directed graph with the Gravatars of people who posted to them arrayed around a central site node, or vice-versa, or a graph of the sites with lines of different thickness between them to denote how much of their community is shared. Then you could look up a site you liked and see what other sites people thought were interesting enough to comment on, which would mean it more likely that you’d want to read, and maybe comment on, what’s at that site too. Or, you could enter in your e-mail address and it could show you other people like you, or maybe graph the network of sites you’ve visited. If you added in the ability for a person to associate an URL with their Gravatar then you could go find out more about the people similar to you.
Visualizing this would be trivial with something like JsViz. The only trick would be deciding how much to visualize. There’s really not a lot to the app itself either, although you’d have to plan for some pretty huge database tables.
Throw in an API for people to query x degrees of separation of sites, or people or anything else interesting and you’ve got a giant ball of coolness. The API could allow them to overlay it with links to the people who were signed up to their TrueLoveForever.com type site and you’ve got some interesting possibilities. Maybe make use of the API free for < 100 requests a day like Google, and other sites do, but charge if anyone wants to make some significant number of queries…. Plus you can always throw banner ads on the site. Heck, you might even make some money off of this.
Obviously this would be easiest for the Guys over at Automattic since they’ve already got the Gravatar infrastructure in place and know exactly what kind of load they’d need to handle before going into it.