Horace Dediu, writing at Asymco:
But the iMac is a historically significant machine. It allowed Apple to start on a new trajectory. It did this by first offering a financial lifeline. Sales of Macs, which were at the time the only source of revenues for Apple, increased from 2.7 million to 3.8 million a year. This at a time when Windows PCs were shipping about 100 million units. That was enough to ensure survival. Today Mac units are five times higher while Windows PCs are about 2.5 times higher. The following graph shows the impact of iMac on the Mac’s trajectory.
The iMac gave Apple the standing it needed to invest in Mac OS X. Without it, the world could be a very different place.