SQL Server 2012
SQL Server Compact based Merge Replication is "supported" by SQL Server 2012, but there are a few "gotchas" that you need to be aware of before implementing this.
This blog post covers these in detail. As you may know, there are 3 components involved in a replication setup: Client, Web Server and Database Server. For each of these components, certain requirements must be met for the solution to work. And each component does not “just work” out of the box.
Client (Windows desktop/server/Mobile)
The client, which can be a Windows desktop or Windows Mobile device, must run a recent build of the SQL Server Compact runtime files. The file version/ServerVersion of the runtime must be 3.5.8088 or later. You can find download locations for the installers of the recent runtime here: http://erikej.blogspot.dk/2010/08/sql-server-compact-35-sp2-downloadable.html
Web Server (IIS)
The SQL Server Compact agent (sqlcesa35.dll) must be version 3.5.8088 or later. You can find download locations for the installers of the most recent Server Agent here: http://erikej.blogspot.dk/2010/08/sql-server-compact-35-sp2-downloadable.html
In addition if you have a separate web and database server, you must install the SQL Server 2012 Database Engine component (and most likely you want to disable the SQL Server service after install) in order to get the required SQL Server COM files installed.
You must also install SP1 and the latest CU, as a minimum CU5. You can find information about the CUs here: http://sqlserverbuilds.blogspot.dk/
Database Server (SQL Server 2012)
You must install Service Pack 1 and the latest CU (Cumulative Update), as a minimum CU5. You can find information about the CUs here: http://sqlserverbuilds.blogspot.dk/
SQL Server 2014
SQL Server 2014 does NOT support merge replication with SQL Server Compact: http://msdn.microsoft.com/en-us/library/bb500342(v=sql.120).aspx – end of story.
But I am working on a blog post about an alternative solution that “just works” and enables you to Synchronize from any device, including Windows desktop/server, WinRT, Windows Mobile, Windows Phone, Android, iOS, Mac OS X and Linux to SQL Server 2008 R2, 2012 and 2014 (even SQL Server Express). Stay tuned, and follow me on Twitter @ErikEJ and subscribe to my blog RSS feed.