Every now and then, I read in forums and in blogs if Sync Framework is "production" grade or if it’s actually being used in real production applications.
Sometimes, I even get asked directly for references on projects or products that are actually using Sync Framework.
Here’s a quick list of Microsoft products using Sync Framework that I know of :
SQL Azure Data Sync Service
Microsoft SharePoint Workspace 2010
Microsoft Visual Studio Team Foundation Server 2010 and Project Server Integration Feature Pack
Microsoft SharePoint 2010