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Microsoft finally released a x64 enabled version of their SQL Server Compact Edition, as part of the SP1 release of it. Previously, the SQL CE was 32bit only, meaning if you were working on a x64 OS, you would have to set the target machine to 32bit. This was especially inconvenient for managed code, as it would default to x64 … well, finally no problem any more 
It will be also part of Visual Studio 2008 SP1, so if you can wait for it (rumours say it’ll come out on Monday) you’ll get it there eventually.
SQL CE is a pretty simple SQL database provider with very nice integration into Visual Studio, allowing you to easily access the underlying database (using SQLMetal and LINQ).
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