http://googleblog.blogspot.com/pdf/Tuzhilin_Report.pdf This is a 47 page report released recently which goes into, in great detail Google's Methods for detecting Invalid clicks & also for Automatically banning publishers. Really interesting read if you've not checked it out yet
Phew that's long. I just read it. Very interesting, thanks for posting that link. The one thing it seems not to talk about much is 'manual' detection - do Google employees manually scour the internet looking at 'click each others ads' schemes or do they rely on their automated filters to pick them up, I wonder? And no, I wouldn't expect google to say either way.