Have buttons "Home", "Menu", "Back" and "Search" in the same order on all phones!!!
I have 2 phones from the same manufacturer (HTC) - Droid Incredible and Nexus One. Released about at the same time (I think) and the order of buttons is different. Switching from one phone to another gives me a headache.
I compared order to a couple coworker's phones (Samsung, Motorola), and the order is different too.