Let's talk about transitions. The Mac in his history has had two major transitions so far.
The first one from 68K to PowerPC (94 - 96). And that transitions happened about ten years ago in the midnineties. I wasn't here then. But the team did a very good job from everything I hear. And the PowerPC set Apple up for the next decade. It was a good move.
The second major transition though has been even bigger. And that's the transition from OS 9 to OS X that we just finished a few years ago at the the early part of this decade(2001 - 2003). This was a brain transplant.
And even though these operating systems are very ename (only by one) they are world's apart in their technology. OS X is the most advanced operating system on the planet. And is to set Apple up for the next twenty years.