John Gruber, professional blogger and podcaster, has been using OmniOutliner for just about as long as it’s existed. His main use is for planning projects — for instance, he recently moved servers, which is something he’s rarely done, and he used OmniOutliner to keep track of the many details and things to check.
He also uses OmniOutliner to collect certain kinds of information. An example is his long-running “Hacks” outline, where he collects and organizes bits of scripts and command-line incantations.
You can find John at his website Daring Fireball, his podcast The Talk Show, and on Twitter @gruber.
Some other people, places, and things mentioned: