Here is my entry:
http://www.flashsoftware.com.au/wordpress/wp-content/uploads/2013/03/BlueCircles.swf
The circles are always circles just sometimes obscured by closer circles. Made up of very large circles with holes in them to see the circles underneath. It might be stretching the rules a little though I hope that doesn’t break them 
The “middle” of the rings of circles follows the mouse cursor with circles further in and further out ease back to the stage center using a Sine curve.
Use the slider on the left or your mouse wheel to change the number of shades of blue used to make up the circles which are then cycled to give some interesting effects from standing still (default) and zooming through a tunnel.
