David, I beleive Janine is in the process of doing just that.
As for 'grep' as a documentation tool, I also rely heavily on it.. but that is definately no way to inspire new users ;)
And of course to 'learn-from-code' does require at least 'some' good introductory docs.
To be honest, in true XP fashion, I'm not convinced of the real need for tech docs and design docs (my opinion).
90% of what people need docs for is when they're new, unfamiliar. They don't want to know how tables are joined, or how request processors function, they want to know how to build a web app, whats important to know, what they can do without knowing, and what the 'process' of using the system is...
