Steve Lasker has a stream of information about this new technology. Start with his Info post and work your way up.

SQL Server Everywhere is essentially SQL Server Mobile with the licensing restrictions removed, so that it can be deployed by client applications on Windows desktops. Thye're delaying release to incorporate a mechnsim for servicing Everywhere on client machines, so that the application can both be ClickOnce deployed and serviced if a security issue is discovered.

Exciting stuff.