We're just starting off with Puppet and EC2, but in general my current feeling is that I'd rather postpone maintaining images as long as I can. This is because a) I don't trust myself to keep these up-to-date, meaning I'll need configuration once the instance is up b) The cost of making a change is tiny with puppet. If you've got images you have to save them again after making the changes. That extra step currently has no value for me, when setting up a machine takes 2 minutes (which is fast enough for us)
