edit- I uploaded a somewhat different spin today on the original concept, more of a cursor toy. It won't be very heavy handed- it's still fairly transparent, but it will look more like a whispy plum that follows your mouse around.
I used the v002 optical flow as part of this setup. I admit, I'm a wee bit uncertain about this one's performance on various GPU's, so let me know if it doesn't work on your system.
It's the basic engine behind this, but the white was a bit glaring for fullscreen, so I made the background transparent- which will mute the look a bit: