I can't help but talk a bit about my own uses for USB, the universalized successor to just about every other external port save for video that was available on the original IBM PCs. My laptop lacks a parallel port, floppy drive, and the two PS/2 ports, but features three USB ports in their stead. What's hooked up to them? A parallel adapter, a floppy drive, and an adapter with two PS/2 ports. Pure genius, folks!
Then there's the issue of incompatibility. I recall, back at a trade expo in the 1990s, seeing somebody with an OCR wand hooked up to a serial port, feeding data off the port into MS-DOS Editor using nothing but MS-DOS's built-in I/O and the ctty command. Palm handhelds that operated over standard serial ports never required special drivers to operate: simply place the handheld in a serial cradle and hit the HotSync button with the client software running on a PC. With USB, drivers are involved - drivers that Palm has decided not to port to 64-bit OSes, aren't supported under Vista, refuse to install if you don't have an accelerated video card, of all things... Need I go on?
My question is this - what exactly is USB doing that original legacy ports couldn't also do, or that other, driverless, more specific standards such as eSATA and Firewire can't do? Why not instead implement PCMCIA or ExpressCard in desktops, giving devices fast, direct access to the machine's ISA/PCI/PCI-E bus without the need to open up the case and install expansion cards?