Here's a great piece of Apple history. In this video (check it out after the break), Steve Jobs gives a demonstration of a NeXT computer. You'll remember that Steve formed NeXT in 1995 after being ousted from Apple. Years later, in 1996, Apple purchased NeXT after Steve's return. Much of the current Mac OS X system is built on the OPENSTEP foundation.
You needn't look too closely to see the predecessors of Mac OS X, like the dock, the services menu, the home directory and windows that display their contents while being dragged. It's also interesting to hear Steve put the Mac down on a couple of occasions. For a nice illustration of how NeXT features became a part of Mac OS X, look here.
Looking at this, one could argue that Steve's dismissal from Apple was the best thing that happened to the Mac OS.