What happens when you get started on a new project? Ever start with a voyage of exciting discovery and end up slogging through two hours chasing down dependencies, watching installers, and decrypting error messages? Vagrant might be the solution you're looking for.
More interestingly, what sort of things can we start to do if setting up a new environment doesn't suck? What would you do if you could instantiate a new project environment at a whim?