A long time ago I wrote a thing called the Temple of Ego. It was inspired by a few other websites but basically the goal was to aggregate all the data you put out on other services, creating an overall stream of all your activity on the web. FriendFeed just opened to the public and it does just that. It's slick and does what it's supposed to do. I'm at http://www.friendfeed.com/bradsucks/
It's extremely simple but there's a lot of potential here. Searching, filtering, shuttling data from one service to another, openID, trust networks. With a nice simple API a lot of services could be built on top of it. It'd be the new meta-Twitter.