I gave it a try a year or so ago because I just *love* these productivity hacks, but it wouldn't fit my mind. The idea itself is great, but for some indescribable reason I didn't feel comfortable with it.
An alternative for speedy dir hopping that does work for me is the cdpath option in zsh[1]. A short-ish description for those that don't know cdpath follows...
For example, in zsh: cdpath=(~/Projects /var/lib/repos)
And with bash(zsh too if you prefer this syntax): CDPATH=~/Projects:/var/lib/repos
From then on cd from any location will allow you to jump to ~/Projects/runkeeper with just `cd runkeeper`. It works reasonably well, including tab completion. zsh definitely allows you to choose whether/how you see the cdpath results in completion lists [2], but I don't know if bash lets you choose.
1. http://zsh.sourceforge.net/Doc/Release/Parameters.html#Parameters-Used-By-The-Shell
2. http://zsh.sourceforge.net/Guide/zshguide06.html#l155
*Edit*: I'll stop posting these overly long comments Real Soon Now™ ;)
I have been playing with it for a few minutes this afternoon but have been annoyed by the fact you have to enter a directory manually with "cd" for autojump to store it in its cache.
The cdpath sounds like a more interesting alternative. Actually I started to dig into zsh a few months ago and it showed lots of promise, I especially loved the built in pager! :)
PS : I hope you will *KEEP* posting these informative comments :)