Using the appropriate tools and design, you'll never have to edit a MANIFEST, and you only have to do a make test for most of the development cycle, I find. (Or a prove -b) Most of the module tools can build a MANIFEST for you these days, and you aren't designing your modules to be so closely coupled that a change in one means a change in the other, right?

Personally, I dislike 'unseen configuration', which I feel environment variables are. And using module tools means it's easier to then use packaging tools, and install tools, and uninstall tools. Oh, and CPAN as well: The modules tools will usually let you just bundle and go.

(One other thing: None of my production boxes have access to my CVS repository. Which would make the 'just check them out' part hard.)