After watching 'Watchmen' I spent several days thinking about how to imitate the "rorschach" effect when I randomly came across http://www.openprocessing.org/visuals/?visualID=4675 . That version is more complete, prettier and better coded, but I was so amazed by the approach that I just had to try it myself...
Curved lines that grow and spawn other lines along the way. I'm almost positive I got the idea from something I saw on openprocessing.org, but I can't find the original, please contact me if you know who the author is.
Left click to start a new line,
Right click to clear and start a new line