I'm very happy to finally announce the long overdue release of SitePlan, my procedural extrusions implementation. There is information about the project here (or just click here to run; java executable; run at your own risk).
Please use the software! The source code is here. This is a research project and it would really help me if you emailed me screen shots of your project and a description of what you used it for.
Here's a very clumsy demonstration video of me using the software:
And some of the kinds of things you can create if you invest a little more time.
With any luck I'll have the slides from Siggraph converted into video any week now...