There is one feature of mobile Safari on my iPhone that I love a lot; it is the one where, when you tap the top of the screen it scrolls straight up to the top of the web page. This is amazingly useful on a mobile browser (I've no idea if others do the same - I would be surprised if they don't).
But more and more I find myself clicking the top bar in Google Chrome (my desktop browser of choice) to "scroll to the top" to, obviously, no avail. So there you go: a great usability feature all browsers should adopt!