The apps I keep in my Finder toolbar are those that I find I want to drop things on--Stuffit Dropstuff, TextEdit, Adobe Reader, Toast, Favorites folder (thanks, Apple, for making the Finder intelligent again about things dropped on the Favorites folder!). I prefer to list locations (volumes, folders) in the sidebar rather than apps. Of course one can argue whether it's better to keep any of these things in the Dock, the sidebar or toolbar of the Finder, or in a third party app like DragThing.

A couple stars off for the somewhat kludgy implementation. It almost looks like the design team forgot they were supposed to PREVENT people from dropping things on the toolbar. The brushed metal design doesn't lend itself to those 2-D icons being laid on top.

2¢ -- Books.