Kingsley Idehen, Uldis Bojars and John Breslin have published some ideas on how to link data from various web 2.0 sites.

Thats exactly what we wanted to implement in gnowsis 0.9.2, although we missed the great looks for it :-) look here!

Here are the blog posts about it

• Personal URIs & Data Spaces
• Linking personal posted content across communities

The idea is to use URLs from OpenID to identify people, a good approach.
Some things have to be thought of:

• It should be connected with the required 303 redirects (a person is not a document, the URL must not return a web document but instead a 303 redirect).
• Not only to aggregate the data, but also to aggregate the ideas. We need to create a personal tag cloud, like we have done in the PIMO

If you dig Java, checkout the aperture.sourceforge.net project to find code that reads flickr, can and should be extended.