From Michigan, I know 548 has used it in both 2011 and 2012 as large support feature's for a four bar linkage.
http://www.chiefdelphi.com/media/photos/36672 had 2 large bar's as supports and 1 large bar for the arm.
http://www.chiefdelphi.com/media/photos/38031 very similar but the have some smaller tubes for a barrel.
I also remember a 2011 team I met at worlds who's robot was almost completely made from carbon fiber.