Have a look at these webcasts: They go from providing a simple but very clear introduction to modeling with and generating code from domain-specific modeling languages to where the technology currently is in making your own DSL editors a very agile task. "Defining modeling languages and code generators in MetaEdit+" clearly shows the necessity of having your models and tools update automatically with language changes.
The API example shows a nice example of what it means to integrate your DSL supporting environment with 3rd party tools, such as an emulator for testing purposes: model-based debugging.
The final webcast shows one of the new features in MetaEdit+: graphical metamodeling, which is helpful during the early stages of language definition, especially when you're working with several language designers in your team. Naturally, MetaEdit+ supports such a multi-language engineer way of working.