I saw a video, I believe it was on Science channel, that showed scientists swirling liquids at high speeds in a large, clear vat. They put numerous coloring compounds of different densities in it and managed to form a hexagon around the pole much the same way it is seen here.
I believe it’s due to Saturn’s rotation and the differences in atmospheric densities and wind speeds that cause this very cool-looking feature.
Prompted by your queue, I did a web search using the words “science channel liquid hexagon” and came up with a YouTube video of an Oxford Univerity experiment illustrating the process:
http://www.youtube.com/watch?v=VQzLY17ncWM