I get maybe a request every two months for a pdf version. It's something I always distantly planned but never thought on acting on it. I'm not really sure how to do it, but after the current chapter I'm working on, I might give it a try.
Try the free for non-commercial use version of http://www.princexml.com/ — you give it some HTML, some CSS and tada, pretty PDF! well, as long as you give it decent CSS...