I'd like to ask a more specific question about Bundler, pertaining to
it's concept of groups.

Do others see this as being truly useful? Or do you agree with me that
it will prove to be mostly a YAGNI, and in come cases could even have
bad consequences, e.g. a requirement was in the test group that
actually should have been in the production group.

Or do you see truly important uses for them, and now that we have
them, would be too inconvenient to live without?