That's really, really cool. I want to make a gallery system for these, where people can submit theirs and others can modify from there. Btw, I just added a polar mode (the grid is treated as polar coordinates, and converted from there); the & instruction switches to polar and _ brings it back to cartesian, so you can actually blend the two.
http://demoseen.com/langton/#&m.$!~PFP!!..