Visual Studio 2008 has been released to web for all MSDN subscribers at http://msdn2.microsoft.com/en-us/subscriptions/default.aspx
VS 2008 includes SQL Compact 3.5 in various contexts, as “Local Database”, and as an ADO.NET Sync Services 1.0 “Local Data Cache”.
VS 2008 allows desktop development using SQL Compact with all editions of VS 2008, including the free Express edition.
For device development with SQL Compact 3.5, VS 2008 Standard or higher must be used.
For an overview of the new features of SQL Compact, see other entries in this blog, and this post from the SQL Compact team: