Also, protected memory will be included in Mac OS X later this year. Macs can't open an application when there is not enough memory. Even if you do, OS 8 determines the application you're most likely finished with, and offers to close it with a click to launch the new app. When formatting a disk, you can't do it in the background. When several applications are running, this can slow down performance.
Macs have perfectly good multitasking.
Whether it's pre-emptive or cooperative makes little difference from the user's point of view. As to performance, you'd be hard pressed to slow down a G3. Only one button mouse for Mac, where PC have standard 2 to 3 mouse buttons. There are lots of them. Also, the other button functions on PCs merely do what option and command keys do on a Mac.