Foopad is an aggregation service for social sites - comparable to Yodlee in the financial space. Foopad allows you to mash-up the various social sites like Flikr, 43things, and del.icio.us, agrregating your content from each service into a single interface (using the APIs each of those services offer rather than screen scraping I believe).
It's cool but there is a price. To aggregate your content, you have to enter your account name and password for each service (once more just like Yodlee). Below is the interface prompting me for my account details for 43things.
When phishers dream at night, surely it must be of pulling something like this off, i.e. getting people to present all their account data in a nice tidy package.
Strangely enough, Foopad does seem to recognize the value of a federated model as they are listed as using OpenID between their subsites.