In-Memory DB for Entity Framework 4

Does anyone know of a good in-memory DB that works well with .NET 4/EF 4? Specifically, I'm thinking of unit testing, such that each setup can easily create the DB, and populate it with default values, and each teardown can destroy it - in a quick fashion.

I've heard that SQLite doesn't support .NET 4 yet, and others have had trouble using it as a substitute for SQLServer (which is what the appliction will run on in release mode).

In the past, I used DevExpress XPO ORM and it had a built-in in-memory database that worked quite well for unit testing.