My question is this: if you invest the time in getting very proficient in a Text Editor like Emacs or vi, what type of return do you get? Please include an estimated number in your answer(ie. I am 10%, 50%, 500% more productive developing Python/Java/Ruby/other using Emacs versus IDLE/Eclipse/Arachno/other).
I continually go back and forth between using an IDE versus using Emacs/vi. I keep giving the latter two a few hours each here and there but haven't invested the time it takes to make it worthwhile. Most of what I write is Python, followed by PHP, JavaScript & SQL.
EDIT: Also if you've written your own editor/IDE, please mention that(it's one option I've been prototyping with).
With Python and Ruby, I find a text editor sufficient and usually I'm doing web work with those languages which is perfect for vim/emacs over SSH.
PHP tends to have a huge library of builtin functions and it uses positional arguments (you can't call a function with arguments out of order denoted by keyword like python). I've found an IDE to be helpful for PHP in the past. SQL isn't a big language. As such, I can't see an IDE helping. JavaScript, with libraries becoming the preferred way to code, doesn't seem like an IDE could do much unless it understood the library.