ex.plode.us bills itself as “social search” but seemed to be to be another social network site that operates by providing links to other social networks that you may be a member of. Not that original, but any site that supports OpenID is worth exploring. It also has a collections and interests feature but I haven’t quite figured out how that works just yet.
I did find one thing, odd. After providing the site a number of profile links, the search came up with two sites: flickr (which I had already provided) and jaiku (which I hadn’t).
For another perspective, read Ian Thal and the Doppelgängers.