Yojimbo 1.0 was just released - by Bare Bones Software (the folks that make the kick-ass editor BBEdit), and it looks like the best personal content manager I've used. DevonThink is overly complicated, and Notational Velocity is a little to simple (but that is also its strength).
Yojimbo takes the best of both approaches, and distills it all into a simple (but powerful) interface on top of some powerful (and elegant) features.
I'll be playing with it more over the next few days, but it looks like I'll be putting in for a license...