Why haven't I seen this coming:
It's a site (currently in private Beta, so I can't really give too many details) that aggregates all the public information it can get from people you consider your friends. You can see what this person added to their Amazon wish list, what they have posted on their blogs, YouTube... And even some things that I didn't even know you could monitor: shared links on Google Reader, favorite songs on Last.fm, things that you dug on Dig... It's quite scary the amount of personally-tied information available out there.
But the concept of the site is quite good, in my opinion. If you have a bunch of friends that are highly connected and use web tools all the time, it would certainly be quite cool to get a feed on what they are up to. I know I miss blog posts from friends of mine all the time (well, ignoring the fact that most of my friends gave up on their blogs - what a shame).
What is the most exciting thing about it for me is that it doesn't limit you to a system. MySpace, orkut, and probably Facebook probably can provide this kind of updates for you in their system; but they can't provide what happens outside their system.
On the other hand, what worries me is that amount of different places that you have to go to keep your list of friends up-to-date. You have to sometimes go through multiple-step registering processes to get each person into the system. And then there is the upkeep (which is probably much more complicated in the case of keeping track of friends' actions on the internet). But we will see. I signed up for Beta testing it and I'll let you know how this turns out.