Org-Mode has been the most rewarding part of using Emacs for me and has been what kept me from switching to another editor for more than two years now. I have a single Org-Mode file[1] that builds my entire development environment.
Same. Every now and then I think "ooh, Acme might be really cool" but then I remember it doesn't have Org-mode. It really is the killer-app of Emacs. I guess it's a good thing because it means I can finally settle on an editor long enough to master it.