Focus follows mouse, but too closely. Basically, if you have focus follows mouse, your alt+tab behaviour is getting screwy. Alt+tab works if the mouse is not over a window, but otherwise, it almost always doesn’t work. Which sucks. To the point where I’m considering going back to click-to-focus as opposed to point-to-focus (recall that I fixed windows to do point-to-focus… windows can be hacked to do this, Unix was doing this, but Ubuntu is now broken. Boo le hoo!).
edit: more relevant bug(?).
edit: I complained about this before :).