It shows you the current folder location in a logical, breadcrumb manner. Hover over part of the current location:
BAM! It fades into a button, and you can click it and hop the folder's view to that location. That's brilliant! (Somewhat less brilliant because it's getting more obscure: (AKA I didn't realize it 'til just now:) click the arrow to the right to hop to siblings of that folder.)
(UPDATE: OSX has a "Show Path Bar" option that brings up a similar breadcrumb-y view. You can even hop up to any of the parents, but you have to double click, which seems unfriendly to me.)
But the really great part is clicking on the location bar just outside of the visible path:
DOUBLE BAM! That is a text version of the path, pre-select for your Ctrl-C copying convenience. Now, even if you're not using the dear old command line much, it's still hugely useful: in any standard file dialog, you can paste that into the filename, press return, and now you're ready to save your file in that location. (OSX sort of does something similar if you start typing with a slash, but it's heart isn't really in it.)
So I don't know if that is a "poweruser" usecase, but I find it hugely intuitive and fast, fast, fast. Now, there are imperfections in this system of text versions of the path-- if you click for a file path when you happen to be doing a search, the result is an unreadable mess that you can't really usefully paste anywhere. But there are other nice touches to the widget that I'm not even going into here.
Speaking of standard file dialogs, here's a bit of crapness from OSX. Here's a file save as dialog.
And so I figured that that functionality must be somewhere in the OSX file dialog, that I could save somewhere other than exactly one of the pre-ordained file locations... but where? How do I get to it?
Answer: that small triangle to the right of the filename. That changes the look of the dialog to this:
(I know Mac fans stuck working on Windows probably miss the 3 column view for its folder viewer, along with the too-cool-by-half "Cover Flow", but for me, I'd rather have the ability to easily transfer path information around. UPDATE: OSX has this functionality, by dragging the icon at the top of a Finder window onto a dialog. Even given my lack of experience with OSX, this seems a little fiddly to me, where I might think I was trying to move the folder to whatever location the dialog was open to.)
Another OSX-ism I find irksome: the default Preview program is great for quick viewing, except it has no concept of "go to the next file in this folder". What's weird is that the basic functionality is in place: it does the right thing if you