I just published the first release of the Esent .NET managed interface on Codeplex.
This is an interop layer can be used to write managed applications that use esent. There is a straightforward translation of the unmanaged API and some helper methods/objects built on top of those methods. I want to develop a comprehensive object model on top of the interop API (which is still very 'C'-style), but that is a long-term project. With the interop layer a primary concern was that this code should be high-quality so it has tracing, good error checking and a comprehensive set of tests that I developed along with the code. The test project currently has ~250 small tests, and there are a few scripts to check the output of the test/utility programs.
I consider the code beta quality right now and plan to push it to 'stable' in a few weeks.