Though it caused some kicking & screaming on the development team, the end result is that every developer has the same development environment, which pretty much matches our deployment environment (in Rackspace Cloud). I also just kicked off our summer intern class, and the interns were able to get productive with our codebase in 1 day despite not having much experience with modern Python web development, because pretty much every local setup step was automated.
I consider the tool invaluable. I don't even install any databases or tools directly on my laptop any longer. With its handy port forwarding feature, you can put all your DBs on a VM, yet still connect w/ CLI clients via your host machine. Then when you do "vagrant halt", all your DBs shut down at once and you free all those resources / memory / etc.
Also, one suggestion -- look into the debug logging level that you can set with an environmental variable. The only thing I found frustrating about Vagrant were situations where it would hang/fail but it wouldn't be clear why. It turns out their debug logging is quite good.