I reported last year about Mob Stocking, the process of ultra dense grazing. In the January 2009 edition of Hay and Forage there is a great article about Grazing Tall, which is where cattle are rotationally grazed in dense populations on mature grass.
The benefits of this type of grazing are increased gains and health of cattle as well as improvements to the soil. For more information go to http://www.carbonfarmersofamerica.com/index.htm