Holy crap I've been working on the exact same thing but for a different platform. This is incredible. We should talk!

my email address is my hn username @mac.com

Which platform, may I ask?

Soon as I get a working ruby 1.9 (hello Ubuntu Hardy!), I'll be giving this a good going over. Looks very handy.

Have you considered using RVM?

http://beginrescueend.com/

I use it to replicate Ubuntu 10.4 server setups on my Arch dev box. RVM does weird stuff with 'cd' so you may prefer rbenv:

https://github.com/sstephenson/rbenv

...though I have no experience of that.

Pretty epic. A pure demonstration of the power of open source. Will definitely have a play with this.