It seems to be a sort of "modular" drum brake, akin to the Shimano roller brake. Modular, in that they seem easily removed from the hub. Looks like they're looking to make the iBrake a add-on option for their 3, 5, and 7 speed freewheeling hubs.
If you're interested in getting a 72p download of the 2005 gear hub lineup (includes the i-Brake and the more interesting i-Light hub), look here:
http://www.sram.com/_media/pdf/sram/...GHS_MY05_E.pdf