@ms I use it for a lot of things. Everything from taking notes while doing research, keeping track of TODO lists etc (I don't use agenda, just like the convenience of having a keybind to mark things as done and the markup ability for bold/emphasized text, and even math equations with LaTeX). I also use it for literate programming examples and tutorials, because org-babel is just so darn good. I also use org-mode for writing posts to my blog.
TL;DR: It's my go-to when plain text just doesn't cut it.
ms