I completely ignore all that social networking stuff; my brain sees them as ads and blocks them subconsciously.
I consider sites like HN quite different, as that is their sole purpose :)
Has anyone noticed the new Mahalo-esque stuff they're doing? All of your hobbies, movies, music, etc... that they're making part of this social graph is now linked together a lot better.
Example, one of my interests (for fun) is "underwater basket weaving" which now links to a page like this, http://www.facebook.com/#!/pages/Underwater-basket-weaving/1...
"Our goal is to make this Community Page the best collection of shared knowledge on this topic. If you have a passion for Underwater basket weaving, sign up and we'll let you know when we're ready for your help."
Pretty crazy.
|http://www.facebook.com/plugins/like.php?*