And yet Apple has managed to pull it off not once, not twice, but at least four times. They've migrated users from 68k to PowerPC to Intel processor architectures -- no easy process, each time. Apple managed to make each change seamless in software to users: With each move, there was a transparent emulation technology in place from Day One.
And the change from Mac OS 9 to Mac OS X, while bumpy for a few years, was smoothed by the Classic environment that allowed the reluctant (like me) to live part-time in the new operating system. We still had the OS 9 security blanket, and could work with mission-critical apps that hadn't been ported to OS X yet.
The iPod , the iPhone and the iTunes Store
The iPod wasn't the first digital music player, not by a long shot, and when the original model was introduced, some people were skeptical to the point of calling it "lame." But it grew into an insanely great phenomenon, and may have changed the world. And the iPhone is shaking up the mobile phone market (no matter what John Dvorak and Steve Ballmer say).
More than just moneymakers, the two have extended Apple's brand exponentially. Wisely, iTunes was made cross-platform (how well it was ported to Windows is another issue), enabling the iPod to get a hook into more than just Mac users. And both gadgets have a "halo" effect: love your iPod? Check out Apple's other fine products!
And even in the world of netbooks, the iPhone could be a first step toward truly mobile computing. It's not a shrunk-down PC -- why would you want a Start menu on a tiny cell phone screen? -- but something new that could work its way up toward a new and useful paradigm. Already, you can use your iPhone to SSH, exchange (but not edit nor save) files, join WebEx conferences, and all sorts of things hardworking people usually need a computer for. I mean, I've longed for a Google implant -- this could be the closest thing for the foreseeable future.
And then there were the stumbles...
The Apple III
Introduced less than four years before the arrival of the Macintosh, the Apple III was supposed to be the "business" computer to succeed the Apple. It made sense to offer a more powerful, more "serious" computer for the more power-hungry, more serious crowd. And Steve Wozniak, a.k.a. the Woz, a.k.a. the other founder of Apple, was in on the design. However, it didn't come together -- literally, in a lot of cases. The circuit board was tightly packed, causing short circuits. One technical bulletin told users to pick up their Apple III and drop it a few inches to reseat chips. And Jobs demanded there be no fan, which caused heat-related problems in the hardware. (Jobs continues to push that anti-fan agenda to this day; maybe he hates the sound.) Other software problems, a high price and problematic backward compatibility with Apple II software all made this a big failure, and Apple's rep in the business world was pretty well damaged.