First, we have to install Homebrew. Once it's installed, we can do pretty much everything else via Homebrew. By default Homebrew will install to /usr/local. It's possible to choose a different directory but everything I've read so far says it's a PITA. I'm sticking with the default.
ruby -e "$(curl -fsS http://gist.github.com/raw/323731/install_homebrew.rb)"
Getting your development environment running requires a few servers. You could get by with as little as Postgres and Memcached but it'll be better if you have Nginx and RabbitMQ as well. Eventually you'll probably want Redis and Artie as well.
TODO: instructions for Redis and Artie