The support for modelling and model-visualization in Eclipse is very impressive, but a little difficult to get to grips with quickly. I had already started working with the free IBM red-book on EMF and GEF when I discovered that there is now a project called Graphical Modeling Framework which appears to subsume EMF and GEF.
Moreover, I'm trying to use the Callisto build of Eclipse (which attempts to combine harmonized plugin and project versions), and the Omondo UML plugin no longer seems to work correctly when used to create EMF models graphically. I cannot seem to add an attribute to a model class in Omondo - the menu command simply doesn't exist. To be fair to Omondo, I think they recognize there are some issues and a forum comment has been posted to the effect that a new version will be released soon for Callisto.
What's so interesting to me is that the Eclipse/Java community appears to be ahead of Microsoft in the area of Domain Specific Languages (DSL) and model-driven development. Microsoft makes a lot of noise about 'Software Factories' and building support for creating and using DSLs in Visual Studio, but this has only recently become available and you must purchase the Team System edition to get it. Team System requires an enormous investment, not just money but also commitment to Microsoft's view of how your team should work and collaborate. Eclipse is free, completely open, and cross-platform. I'm going to be looking in more detail at the libraries and tools for doing model-driven development, and building graphical editors.