In a moment of somewhat unexpected nostalgia at its most recent media event, Apple pointed out that it was the 25th anniversary of the PowerBook. (It’s good to know that, 27 years later, Apple still would rather nobody remember the Mac Portable.) I’ve been a Mac laptop user since the original PowerBook era. That ancient history is my history. Since 1991, Apple has gone through seven distinct eras when it comes to its laptop strategy and design.