One thing everyone would notice on attaching a USB mouse to an Android device is that mouse wheel is not supported, which makes interaction very tedious. I take a quick look at the state of its support.
Android-x86 project advertises mouse wheel support, but looking at their patch, they translate mouse wheel clicks into up/down buttons. That's better than not supporting wheel at all of course, but still not intuitive usage. What I'd like to have is not analog of up/down key press, but actual scroll, i.e. analog of drag.
But probably, such behavior couldn't be reliably emulated on the lower level of input processing, (or this might lead to adverse effects, like mouse wheel movement interpreted as click). Instead, higher-level controls should have explicit support for discrete scroll events. For example this event handler block should be factored out to be callable for such event and be passed just deltaY.
Of course, that would be more or less big refactor, so another approach would be just waiting until Google thinks it gave enough competitive advantage to big vendors over small and finally releases 3.0+ source code, which supposedly implements wheel support.