I gave a talk today announcing the public launch of the MyBlogLog API. The is the only API that I know of that allows you to look-up a person’s identifier across social networks. Read the docs here.
Other URLs from the talk:
Blog Juice – a bookmarklet to look-up social activity of recent reader.
Raven SEO – a working example of a portable, social network
Meetspace – using Bluetooth to discover which MyBlogLog members are in your proximity
Update: Slides from the talk posted on Slideshare.