The final v1 spec for Simple Sharing Extensions has been published under a new name, FeedSync. The new name is a little simpler than the old one (kind of ironic!) and it captures the intent pretty well. A new site at feedsync.org explains what it is all about. The initial specification described how to synchronize data through Atom and RSS feeds.
A simple FeedSync sample project has bee posted on CodePlex. Look for the FeedSync Samples project.