At CHIP, my team and I have created a new Web application modeling and Code Generation framework called Clickframes (http://www.clickframes.org/). It would be interesting to see what other people are doing in this area.
My experience of Model Driven Software Development:
I am the Lead Developer of Clickframes, at CHB, Harvard Univ. affiliate).
Clickframes is a way to model web applications via a single XML file. Once you have modeled your application, you can generate code/tests/previews/flows and much more using various plugins. Generated code is readable and can be customized.
It has a open plugin architecture which lets third party create their custom plugin.