A bit different, but I really appreciate when web apps use the HTML5 history API to implement back buttons, e.g. Twitter. It makes the history queue that appears when long-clicking the back button so much more useful.
Too bad that other sites use the same API to forbid you from going back where you came from, by filling the back stack with hundreds of bogus entries.
I remember some browser blocking that at some point, but I still occasionally see it. I can’t believe there’s no way to “go back to the previous website” in most browsers. Safari iOS for example just clips the history so you can’t even hold the back button and scroll up if there are dozens of entries.