Bah, firewire!
Okay, with that out of the way....
USB 2.0 is wonderful for storage. Thumb drive, memory stick, ipod, external hard drive... all great. USB 1.1 is perfect for other peripherals. Keyboard, mouse, gamepad.
One thing to keep in mind is that a 1.1 device will work with a 2.0 port, and vice versa. However, plugging a 1.1 into a 2.0 can really slow the entire thing down depending on how it was made. So if your hard drive still seems slow, check whether your keyboard is plugged in next to it.
But yes, USB is a wonderful idea. As to why it took so long.... well... let's put it this way. For many years, both the keyboard and mouse had identical connectors (mini-DIN), but _did not_ work if you plugged them into the wrong ports. Color-coding was a relatively new invention. Computers easy to use? Heh.