Friendfeed was the first social site that I remember that enabled/encouraged the makers of products to directly communicate with their audience. Very producthunt-esque in that way :) I believe they were also the first site to offer a "like" button. It wasn't appreciated because it required its users to be extremely active online (aggregate all your social activity was its selling point - but if you only used one or two social sites, Friendfeed didn't serve much purpose). Because I'm a product dork, I've actually written about this before:
http://www.quora.com/Why-did-the...http://www.quora.com/What-are-ex...
- - - -
Misc info: the product was made by the makers of Gmail (Paul Bucheit) and Google Maps (Bret Taylor), and sold to Facebook because Google was about to launch their first social site (Buzz). This seemed like a big threat at the time because everything that Google shipped turned to gold in those days. Nobody would have guessed they'd struggle so much with social products.
Cuey