cool!
although as you say, it gets confused if new windows appear, i have to say, its quite cool, and in fact just using it for a second or two, you can see that it is a neat idea for a program, and maybe one worth taking the time to write in visual c++ for optimum speed.
i had real doubts about whether this would be anything but an annoying thing to use, but it's actually kind of a fun effect, that might be worth spending some time on.