In an excellent article, long-time tech journalist (and Internet Press Guild colleague) Wayne Rash explains how forthcoming quantum computers could render most computer security worthless. I won't go into the details — he does a great job at that. But in short, quantum computers can solve certain kinds of problems instantly.
I got the idea from "Almost a Brain" after learning that the world's top supercomputers are nearing the level of raw power in our brains — about a billion billion (1,000,000,000,000,000,000) operations per second (an "exaflop"). I've since come to recognize that there's a lot more to brain modeling than power, but supercomputing still has a special place in my heart.