I have about four keyboards (generic Taiwanese-made brands), all of which work with the CCK USB, and about the same number which don't. (I have a fairly extensive collection of keyboards.)
just to add in more. using powered usb Ive successfully able to use the ff:
zoom h1
a guitar pedal zoom g2.1u and i am sure the newer ones shouldnt have any problems
a 16gb flash drive from sandisk cruzer
as of the moment, only my hdd (even formatted to fat32) is unsuccessful