For the past 2 weeks or so, I have been learning Emacs, something I've been meaning to do for years now. I decided to do it seriously (not skip a day, sometimes hours at a time), and am really liking it. It's a very well-designed application with a great amount of polish, far more than anything I've seen yet (I've used Vim, Geany, Scribes, and Eclipse). It also helps that the documentation is so well-written.
So far, my single most favorite feature is Auto Fill Mode, which allows you to keep typing without caring about line breaks, for they get automatically get applied for you. Am very sure that this feature exists elsewhere, but I actually never used it.
Related to that is the fill-paragraph command, which is invoked via the Alt+q shortcut (M-q) in Emacs speak. What it does is reformat the paragraph as if it was typed while in Auto Fill Mode. Is gorgeous!