"I found I was much more productive in Ruby with a simple editor than I had been with other languages plus an IDE"
Bingo, and that is why we do not see fancy IDEs for agile languages. The corollary being horrid languages have great IDEs because lawdy we need something!
One thing going on here is reflection. If my language has that I can toss off my own rough IDE-ish hacks in minutes and then they do exactly what I want, too, so the demand just never develops for off-the-shelf IDEs.
I work with tens of KLOC of Common Lisp at a time. I like sitting in a backtrace and using a keychord to jump to a functions definition, or sitting in the inspector and jumping to a class definition in source or with a diffeent keychord to the class in a graphical class browser. ACL integrates everything (except, strangely "who calls?", tho that is available via an unexported function), so I just sail all over my big code bases as fast as I can think, click, and keychord. Some folks, btw, feel the same about Lispworks and Slime, we need an IDE smackdown some day to comapre. :)