I'm interested in use cases for netmodules in .NET. In particular, I've been looking into better ways to break up solutions in .NET but not have quite as many assemblies to deploy. Netmodules are a very interesting idea, but they appear to break debugging and are not natively supported in Visual Studio (though they are for MSBuild). I'd prefer to rely on something native to .NET, so ILMerge, while interesting isn't what I really want.
For some of my own projects, I'm also beginning to use FAKE, which allows for some interesting build steps, such as separating out test files. In other words, writing custom compile steps is not a problem.