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We just got an invite to BlueSwarm, a new social network aggregator "built by three guys in their spare time". It's in private beta, and fairly feature-light right now. In theory, you can enter you username and BlueSwarm will try to find your profiles on social networks (didn't work for me, but manual addition did). You can also create a feed from those social profiles and explore content from friends - there's a Flash widget of this feed, too.
It's very basic for now, but give them some more development time and this one may be pretty useful. French startup Ziki began with a similar premise.
Disclosure: MyMashable has a social network aggregation feature.