I really like the way it lets you navigate from function to function (and file to file) and back again. What would be even more useful would be to have a "history" window, similar to your browser's history, that would show the list of files/functions as I'm navigating from one to the other. This would allow me to step forwards or backwards, or even jump to anywhere in my navigation history, without having to slog through the open windows.

Note that this "navigation history" I'm thinking of would be completely unrelated to my edit history; undoing and redoing an edit would not bring me forward/back in my browse history, and vice-versa (although there could certain be keyboard shortcuts for traversing the navigation history as well).