Mouse Gestures is a horrible idea. I routinely wave my mouse around the browser window when I browse, highlighting blocks of text. Just a habit I've got into. But the LAST thing I want is the browser interpreting my gesture as an instruction.
I hate those wikis which interpret any click on a non-link as meaning you want to edit the page.
Also I notice that the MouseGesture example seems to break arrow key scrolling.
I hope this doesn't take off ...