This sort of thing led me to doing all development on a per-project Linux virtual machine. I started by using various development stacks (LAMP, LEPP, whatever) running under VMWare Fusion, using appliances from http://www.turnkeylinux.org/ or http://bitnami.org/. Then I discovered Vagrant (http://vagrantup.com/), which is a nice command-line driven tool for managing and provisioning base images. I use it for everything now.

You can run Lion virtualized under OS X, if you are so inclined, but I don't see any advantage to doing so.

I like the isolation of environments so much that even if I were to switch to Linux as my day to day OS, I would still develop every project in a VM.