It might be just me, but off the top of my head, I can't think of anything that would actually be able to use that sort of throughput. Surely it's just moving the data bottleneck to somewhere else.
Can any disks write that fast? Even if they can, if you have an external disk, the connection to the host PC might be USB, but the actual connection to the disk is still likely to be SATA, which is slower, right?
I might be missing something really obvious, but other than external disks (and networking, bust as mentioned above networking over usb has it's own issues), I cant really see the need for that sort of throughput on an external bus.
Printing? Mouse? Keyboard? Web cam?
Just because everyone loves a car analogy. To me, it seems like having a car that can go 500mph. Great, you have the fastest car in the world, but there is nowhere you can drive it at that speed.