Activity Monitor tells me my single VM running in the background is taking up less CPU time than Skype (which is also idling in the background).
10 minutes later I was back in business like nothing happened.
Had a physical machine of mine failed it would have been a fun few hours of machine debugging, instead of "oh, I'll just destroy and recreate the VM, no biggy"
On mine (https://github.com/drench/vagrant-base) each branch sets up a different environment (Drupal, node.js, generic "LAMP", etc.). They currently all use shell scripts for initialization, but converting them to Puppet is on the list. I may borrow from your project's Puppet manifest.