Org-mode is what finally converted me to being an emacs user.
I'd been searching for a lightweight, console/cli-mode outliner/task-manager when it occurred to me "surely emacs has something for this". It did, of course.
For several weeks I used emacs only for org-mode. Slowly but surely emacs started to take over my more and more of my editing tasks. Now I find myself not even bothering to launch X, but simply emacs from the Linux console (run level 3?). It's amazing how responsive a computer is when you're not using any gui at all.
I've since discovered that org-mode is pretty common gateway into emacs.
My favorite Emacs feature that I've learned about in the past year is Org-Mode. I use it now for just about everything.