For those of you who didn't hear about it yet, Google announced its Social Graph API. The purpose of it is to use XFN, FOAF, and OpenID edges that Googlebot comes across to create a huge graph of relationships amongst people online. It also makes connections between your various online properties so that your connections within your own part of the web are covered as well.
It leads to some cool possibilities. For instance, I use FriendFeed to aggregate all of the content I create online. It's really handy to have that master list of services and have it just take your username for various services over having to plug in every atom and RSS feed I contribute to. But beyond aggregating my content, it also lets me know what content my friends have created. Using Social Graph, FriendFeed could theoretically go to my blog, find out who my friends are, and then find out what content my friends have out there and then create imaginary friend accounts for me that covers their content until they get FriendFeed accounts themselves.
This has the possibility to allow me to ditch social network sites. I honestly only care about sites like Facebook to keep on top of my friend's content (and to make my girlfriend happy since she is the one who pushed me to open an account in the first place =). By using best-of-breed sites for stuff (Flickr, Jaiku, Blogger, etc.) and Social Graph for the social connecting, I personally don't need Facebook for anything.
But obviously the trick is making all of these connections. Sites like FriendFeed and Jaiku that aggregate your content help take care of connecting your content together. But how best to make connections with others? While I have gone ahead and added a list both here and on my personal site of people whom I know with links to their blogs that I read, I don't expect everyone to know how to make an unordered list in HTML. The various points-of-contact for people online (which is typically one's blog) will need to grow basic support for people to easily toss in links to their friend's and specify that they are in fact friends.
In terms of FOAF vs. XFN for the markup to make these associations, I prefer XFN. I want the simpler solution that most directly draws connections between my content and between me and my friends. I don't need everything that the FOAF spec supports; it seems designed by committee to be very specific to the point of it being a detriment. XFN has the right level of detail (although I could do without stuff like "muse" and "crush" associations) while be generic enough to not be as verbose as FOAF.
Here is to hoping this takes off.