I've become a huge fan of org-mode and muse-mode. I use muse-mode, which I discovered before discovering org-mode to manage a local wiki where I keep mostly work-related notes.
I use org-mode to manage my tasks and use it to take notes. As a task manager I've found it unbeatable. I intend to migrate my muse-mode notes to org-mode "any day now" ... well, as soon as I get around to hacking up a python script to convert the links for me. I'll miss some of the more wiki-like features of muse mode, but I think in the end I'll profit from having everything in org-mode.
For me, it replaces OmniOutliner and OmniFocus. Plain text. Works on any platform that supports emacs. Easy kept synchronized between computers using source control. What's not to like?
