This could prove to be a real winner, if it catches on and can be made to work effortlessly -- particularly if it becomes an open standard.
If done right, SSE could provide a generic and non-proprietary form of two-way synchronization between any two sources.
I'm a big fan of the excellent Lotus Notes replication model (particularly since Release 4, when replication became sensitive to field-level changes not just document-level changes). Notes replication of course is quite proprietary, so it would be great if SSE provides a form of non-proprietary replication between foreign sources.
Ray points out the draft spec for SSE (somewhat abstruse as are all such specification documents), and Frequently Asked Questions (this is quite informative).