http://jtimberman.posterous.com/more-dynamic-run-list-testing-with-vagrant

We're using this technique internally to have one vagrant box that can spin up a site-as-an-install-profile from any installation profile.

So for example, you can do "project=myclientproject vagrant up" and it will spin up the VM, clone our git repo from git@github.com:myplanetdigital/myclientproject.git, then run drush make and site-install (assuming the profile is named "myclientproject" as well) on it.

We've also got an includes/ dir in the installation profile, and contained files of format *.settings.php get appended to setting.php, so it's simple for devs to add to settings.php, and still works with our deploy process.

I'm realizing there's lots of overlap, so I'm really going to try to clean our vagrant repo up so I can help out here :)