The Sync Framework 4.0 (they jumped over the v3) October CTP is available for download. This framework is built on a top a standard protocol - OData and implements an "assymetric" syncing - meaning that most of the synchronization logic will be running on the service side. The release includes server and client components that make it easy to build offline applications on Silverlight for desktop and WP7 platforms. The CTP also ships with samples that show how to use the framework in Silverlight, WP7, WM 6.5 and HTML5. In a few weeks there will be a refresh to this release that will add some tooling as well as the sample for IPhone.

Enjoy:

http://www.microsoft.com/downloads/en/details.aspx?FamilyID=afd89099-d589-423c-9762-78096aa95ac2&displaylang=en

http://msdn.microsoft.com/en-us/library/gg299051(v=SQL.110).aspx