A fresh installment in Ted Gornason's About This Particular Outliner emphasizes workflow, but includes a thorough survey of current outliners. Goranson's series is arguably the most intelligent and thorough examination of a software sector ever attempted.
He says some nice things about Tinderbox, too.
Tinderbox is the most capable of the power outliners in most respects. It has remarkable smart agent capabilities, clones, and links. It can shift between outline view and several graphical views, most notably a “map” view where headers are boxes that “contain” other boxes. Since its appearance, it has always been the king in terms of most features plus its internal scripting language...
...We think this has the best user interface conventions for the things that matter: dragging, cloning, linking. The map view is the most Mac-like spatial thing we’ve ever seen.