what marctronixx said.
requests to add usb-host capability are all over the android dev forums, and software-wise it's actually not very difficult to implement.
the problem is convincing the manufacturers that adding the hardware is a good idea. many simply come back with 'bluetooth can already do that', but if you've ever tried bluetooth file transfer you'll agree that bluetooth can almost never 'do that' acceptably.
usb host would open up a massive array of available peripherals, from keyboards to external sound cards, usb storage and even all those crazy usb gadgets (if only my hero could chill my beer!)
photography is another huge area for this kind of interoperability - it would be unendingly useful to snap some photos with your good DSLR, plug it via USB to your Hero, and send those pictures anywhere on the internet. rare is a camera that will support bluetooth file transfer - and you definitely don't want to do that with a 10mb+ image.
definitely on my wishlist for the next android phone.