I just recently bought the usb flash drive for my xbox 360, as both previous reviewers (bigup7 & toetag) have already mentioned the main points about the flash drive, I am just going to let you know a few things for those who also intend to buy it for their 360.
First, You do not need a usb for the 360 that is 16gb, you just need one that is over 1gb.
Second, you will not be able to copy your gamer profile to the usb but only move it there, most games save are both transferable and copyable. You will not be able to copy/transfer other gamer profile except the one you are signed onto. Which means you will have to sign onto the different gamer profiles before moving it to the usb.
Thirdly, Copying files/saves from your xbox 360 is a long process however just transfering it is much quicker, by that i do not mean the writing time of the usb, i mean the process in which you will have to manually select which files you copy.