ESENT - Embed Database for Windows

I never knew that. But it seems Windows has an Embed database with it which sounds really interesting (no more MsSqlExpress, FireBird etc).
It also has a .NET interface at CodePlex.
This sounds interesting, but I'm not sure how reliable it is and what are the exact features (bugs) of it.
Also when most of the O/R-mapping tools will start supporting it (the ESENT API has already been published for years).
Anyway, I'll need to have a look at this type of DB but I'm a bit skeptical about using it in a real .NET project.