Bungie mentioned in their new podcast. Halo 3 will not ship with clan support. As Frankie puts it, the clan support in Halo 2 really amounted to no more than a second friends list. The Bungie boys don't rule out the possibility that Halo 3 may support clans in the future, but don't expect to see it in the retail box next month. Oh, and don't forget that Microsoft isn't planning on implementing cross-game clan support anytime soon either.
But here's some leaked images courtesy of Iceman: