Nicely complicated--- useful if the boss or client wants verbiage. If asked directly though, I usually say "If I've done it before, I know how long it takes; if not then not."
My post is definitely not suitable for most management, but in a discussion with a bunch of fellow geeks, it did fit in with the discussion.
Explaining this to management/clients is not easy. It's a problem that needs tackling, but it's a separate problem.