To coincide with the RTM release of SQL Server 2008 the SQL Compact Team have delivered Service Pack 1 for v3.5. This includes Entity Framework support and a native 64bit version. Steve Lasker has the details:-
http://blogs.msdn.com/stevelasker/archive/2008/08/07/sql-server-compact-3-5-sp1-released.aspx
Meanwhile SQL Server 2008 RTM is available already online for both MSDN and TechNet subscribers.
Read the complete post at http://feeds.feedburner.com/~r/PeterFoot/~3/358569584/sql-compact-3-5-sp1-rtm.aspx