FireWire
This is sure to enrage a few people, who will almost certainly point out that FireWire is quicker than USB, has a more sustainable speed and is still common on Macs. But the truth is it's not as popular as USB, and it never will be.
For some reason, despite the incredibly shaky start USB had -- we can surely all remember the near certainty that plugging in anything in the early days of USB 1.1 would result in either a blue screen of death or some other virtual plume of smoke -- it still managed to beat FireWire to be the most popular data-transfer system. Sure, you could argue popularity isn't everything, but try telling that to all the dorky kids at schools across the world.
For the time being, FireWire lives on as a way of transferring video from camcorders to PCs, but as time goes on and USB gets ever better, and wireless, we'll see the eventual demise of FireWire. At the very least, it's on the verge of obsolescence.


