Here are the three things I found most interesting/relevant/useful/cool:
1. Social graph API - Brad Fitzpatrick introduced the Social Graph API on Saturday morning. Check out the resources on the Google code page to learn more about it. My view is that this seems to be going in the right direction thus far, though I'd definitely like to see the rel="me" claims getting verified via OpenID. I'd also like to see applications access non-public friend markups via OAuth.
2. Open Activity Streams - David Recordon led a session on the recent MovableType Action Streams release. I predict that Activity streams (or social event aggregation) will be the next big area for innovation in 2008. The idea is simple - I should be able to view (and eventually, create) all events that are relevant to me in a single place, instead of having to navigate to each and every social network/web application I use. Similarly, my friends should be able to remain updated on my activities across the internet - things that are already visible to them, albeit not without significant work today. I'd like to see standards emerge here around the messaging protocol, data formats, and authentication/authorization mechanisms. Good news is that the open standards on which this could be based already exist - its just a matter of combining what we have in a way that makes the web a more interesting and useful place to be in. See this and this if you want to learn more about Activity Streams.
3. Doing something useful with the OpenID URL - Late on Saturday night, I led a session titled "What can I do with the OpenID URL?" A bunch of us got together to talk about how we'd like to see the OpenID URL used to provide more useful services - both as end users of these technologies and as the people responsible for these products in our respective organizations. To start with, we discussed how having a useful profile on the OpenID URL endpoint would be valuable. We then discussed the potential use of the OpenID URL as an endpoint for permissioned messaging. Imagine that OpenID Relying Parties can contact the user by using the OpenID URL - which the user has proved ownership of - this brings the user back in control of communications - he can turn it off at any time, direct it to his voicemail (text to speech) between 12 pm and 3 pm, etc. etc. We then discussed the general use of the OpenID URL as a service endpoint (or more appropriately, a service discovery endpoint). Heres a picture from this session.
Brian Ellin ran a good session on improving the OpenID login experience. I was also glad to hear that our efforts around making the OpenID login experience easier (by allowing users to simply click a button to login with OpenID or to type in yahoo.com in the OpenID textbox) were generally welcomed by the folks present there. Theres nothing like direct user feedback - and its even better when its so positive!
All in all, this was a weekend well spent - its always enjoyable to meet so many folks committed to making the web a more fun and useful place. Many thanks to Scott, David, Tim O'Reilly, and all others who helped make this event happen.