I'm pleased to announce that, after a very busy weekend and one or two weeknights, I've successfully built a Python equivalent to the Google Web Toolkit (GWT) that can handle half the Hello World example.
It sounds small but the pieces are largely all there in a primitive state:
Now it's just a case of incrementally improving each of these areas.
You can see the result in revision 19 at:
http://pyworks.org/svn/py-gwt/hello-experiment/
Join the mailing list if you want to get involved in any way.
UPDATE (2006-05-26): The project now has a name and a website: pyjamas