In this article in the WSJ- http://online.wsj.com/article/SB1000...ions_lifestyle American studied how to improve boarding speeds and based off of 1000's of observations and computer simulations, random boarding is the fastest (after Elites, of course) compared to back to front or even window, middle, aisle order. This was implemented in the US and Canada in May and since rolled out in Europe and Asia. This all also occurred when they went from 10 boarding groups to 6..

Other benefits touted were:

20% less checked baggage at gate
"Calmer" boarding

Other airlines are apparently monitoring AA's success with this new process.