We discovered that multiple database types in a single nhibernate project didn't work in practice: the code of databases enumerated later on in the code generation process overwrote the already generated code. This was due to a problem in the presets: it should generate the code per database in a specific folder, if required. We have addressed this in the upcoming build.
It was discovered that when using multiple groups and the grouping mechanism is set to AsSeparateProjects, the vs.net project name generated wasn't reflecting the group, but always had the 'projectname' as its name. This has the disadvantage that when you add all vs.net projects to 1 solution, you get conflicts and it doesn't work.
We've changed this to be the group name in this case, or more importantly, we changed the [projectName] directive in the presets to [containerName] as it should have been.
We added N:M support for NHibernate to the upcoming build as well.