I've started developing in my "free" time and as part of that I decided to fix the screwed up installations of MacPorts and RVM that I had on my primary laptop.
My machine has been so screwed up I've been developing for a while using a Linode instance, ssh tunnels and ExpanDrive. This solution has worked pretty well except for an annoying issue with TextMate freezing every time the application got focus when I had an ExpanDrive based file system opened. I started with blowing away my old installation of MySQL, MacPorts and my previous system-wide installation of RVM.
The new development tool chain uses Homebrew, RVM, and Vagrant. Hopefully the time I had to invest to get to this point will encourage me to keep things clean. The idea of building isolated VMs for project development seems solid and a number of people I have some respect for seem to be using vagrant successfully for this purpose.