One of the main differences between early PCs and early Macs was that the PC had two serial ports called COM1 and COM2 and a parallel port for the printer, while the Mac had a 9pin serial port for the printer and a telephone cord-like connector for the keyboard. These two flavors of serial port were eventually superceded by the USB connector on both machines.
As the Mac world looks to an upcoming shift in hardware in two years or so, questions have arisen about how the serial ports might change. There are immediate consequences for hardware purchases, especially for buyers looking to keep and use their peripherals even though the underlying computer chips may change. Heres my take, viewed through the cloudy crystal ball I keep around for just these occasions.
I think USB 2.0 will be the primary way that the new machines will communicate with the world, along with Ethernet. Firewire ports will be around for a while, but their utility will diminish over time. Firewire (IEEE 1394) has never really caught on big time in the PC world, even though it is a great way to interface with peripherals that transfer large chunks of data (like digital cameras).
This may well be because the PC computer makers have not included it as a default feature on a machine. It has been necessary for the owners to add it themselves as a card on the motherboard, and your Aunt Ethel doesnt know how to do that kind of thing.
USB, on the other hand, is a default presence. Its there on any new machine, whether it is a PC or a Mac. That means peripheral manufacturers will design in its use, just to avoid having to make two kinds of interfaces.
That desire of the manufacturers is a great part of how the port came into general use in the first place. USB has gotten faster as the specification has matured and is now able to do reasonably fast transfers.
Of course, external hard disks and the like run faster at the higher data transfer rates of Firewire; but it seems to me that the current trend of computer makers including humongous internal hard drives will continue. This reduces the need for add-on mass storage, and the need for the higher speed connections that support this kind of peripheral. Not that it will ever disappear, mind you.
There will always be a demand for some way to store huge digital video files and the like. But I think that the main hard drive (especially ones that take advantage of faster internal buses) will displace the box hanging off the side of the machine.
Apple has learned well the lesson of the iPod, which uses USB so that it will run on any machine. I think any future consumer products from Apple will be USB-based as well, just to be able to run on any platform you have now or may have in the future. So, USB looks to be a safe bet for the next five years. It may not be the best technological solution, but it looks to live up to its moniker of universal.