FOAF was one of the first Semantic Web projects, and is still trotted out as an example on a regular basis. The FOAF model itself has been criticized a number of times (I don't feel like googling all the examples), but there are some things about FOAF that are very interesting in today's world.
One could criticize FOAF for having invented social networking in the late nineties, then having missed the whole Web 2.0 boat, to have the limelight taken by myspace, linkedin, livejournal, and nowadays by facebook. Indeed in terms of bringing social networking awareness to the masses, this criticism would be true. But if you have a look at some of the founding assumptions behind FOAF, you'll find that the project was eerily prescient - forseeing problems with social networking that took years to come to light once social networks became commonplace.
A simple example is a bit of drama that happened on the social networking site LiveJournal a couple of years ago. Livejournal was sold to a Russian firm, with the risk that all the servers, with all those back journals, would migrate outside the United States. Many American users (who for the most part had been ignoing the vast number of Russian speaking users) suddenly became aware of the fact that their precious journal data might drop out of control of copywrite laws that they understood. A panic ensued, and LiveJournal dump programs became quite the "meme".
FOAF understood this issue over a decade ago, when they envisioned a distributed social network, where servers owned/operated by different agents could participate in the same social network. A sort of decentralized, distributed version of facebook. Where you kept your own ownership, access control, backups, etc. Or you could hire someone to do it for you, if you preferred. But you had the option.
This is a key idea behind the Social Web - not just social networking on the web, but making the network part of the web itself. How can this work? The Semantic Web plays a big role in the solution - or so many of us believe. Come to the Social Web Camp in Santa Clara on November 2 and find out what the W3C and others are doing to make this come true.