[tedsanders]

Yeah, one interpretation of what a quantum computer does is that it performs all computations in parallel. However... you run into problems when you try to read the output of this computer. In order to read the output you must measure a quantum state, and when this happens you only get to see one answer at random, not all of them. And that's not really useful. But if you can design an algorithm so that all of the parallel computations add together to form one answer (i.e., get all the wrong answer's probabilities to cancel out), you can get an exponential speed up. The key takeway is that quantum computers are not faster for general problems - quantum computers are only faster for problems where a special algorithm exists (like Shor's algorithm for factoring).