I have updated the Group navigation state-of-the-art report with an interesting article I read a few weeks ago :

Qin Gu and Zhigang Deng. Formation Sketching: An Approach to Stylize Groups in Crowd Simulation. In Graphics Interface. University Houston, Delmar Thomson Learning, 2011. 

I've also set up a static page for the report at www.crowdscontrol.net/pages/group-navigation-state-of-the-art-report