One of the signs of a maturing discipline is that change gets slower. I'm think that IT is reaching that point.
I mean, what can you do today with IT that you couldn't do three years ago? In December 2004, you were operating Windows XP, Firefox 1.0 and Office 2003.
Despite the release of successors to all of these software packages, the features available are still pretty much the same. Really, we've just seen new coats of paint and a few usability improvements. The Internet's still the Internet; word processing is still WYSIWYG; and operating systems are still pretty reliable.
Chronologically, I'd mark these as the major "tipping points" of IT in the last 25 years. These aren't necessarily the first time the concepts were invented, but they were the point at which they crossed into mainstream acceptance: