I did the same thing. What's nice about the Phoenix approach is that you start with a known state (base Ubuntu install or whatever) and end with a known state (running your setup) and completely ignore all other possible states. A tool like chef or puppet has to have a lot of complexity around examine a node, determine what state it's in and figure out how to get it to the desired state.

I also use boto in my fabfile, so that I can run a single command to launch an EC2 instance, install & configure software on it, save an AMI and terminate the instance. It's a like having a Makefile that compiles machine images:

    > fab build:<role> <region>

I wouldn't go as far as Fowler's "disable the shell" idea, but it doesn't take much discipline to do all significant changes by building new AMIs.