Chances are you use at least two major social networks – 49 million people, for example, visited both MySpace and Facebook in October 2008 (Comscore, worldwide). Nearly 7 million people in the UK use both Bebo and Facebook. A lot of people maintain very different friend lists on LinkedIn than MySpace or Facebook. Etc. And when you add in niche social sites like YouTube, Flickr, etc., there’s even more overlap among users.

There has never been an effective way of aggregating and merging all the data and activity on these sites into a single user interface. A new venture backed Brazilian-based started called Power.com launches today, though, that aims to do just that. They’re calling what they do “social inter-networking” because it allows users to view and interact with all of their social networks at once. Data is aggregated, and the sites themselves, if accessed via the Power.com site, are marked up with added features in a way that Greasemonkey users are familiar with.

The service is unknown in the U.S. today, although it’s been live since August and boasts 5 million users already. Until today it supported just a few social networks, notably Orkut. Now, though, the service supports users from Facebook, MySpace, Bebo, Orkut, Hi5 and a number of niche networks like YouTube.