What would you do with 128 programmable quantum bits? If you're not certain, perfect, that's just what it's designed for. Just for heaven's sake don't look at it or it'll stop working. Yeah, welcome to the wonderful world of quantum mechanics.
The D-Wave One is the first commercial quantum computer. It's for sale, and you can buy it, although D-Wave isn't saying for how much, so it's probably absurdly expensive. What makes it unique is that it does its processing using 128 qubits, or quantum bits. A qubit is just like a regular bit, which is one of the things in your computer that switches back and forth between zero and one, except that a qubit can be zero, one, or both and neither at the same time.
This bizarre property is called quantum superposition, and it can be used to solve some specific sorts of problems using a technique called discrete optimization. It's particularly handy for classifying small pieces of larger data sets, like figuring out whether an image contains something that looks like a car, for example.
I'm not sure if anyone can adequately explain just how a quantum computer works, but the basic idea is that you program the computer by translating your problem into a series of coupled spin states between quantum bits. Once you've set up this network of qubits, 'running' the program causes the qubits to undergo "quantum annealing," where they all move towards a low-energy state, and once they reach that state, your problem is solved.
One of the tricky bits about quantum computers is that if you actually watch them doing what they're supposed to be doing, you ruin the computation. You've probably heard of Schrödinger's Cat, where the cat is both alive and dead until you check to see which is the case: it's the same deal with the computer, which gets its magical powers from that quantum weirdness that keeps it in multiple states at once. And as soon as you check, poof, it's gone.
D-Wave has managed to verify that their computer can actually do the computations that it says it can by taking super fast snapshots at different points in the computation. This stops the computer, of course, but by running the program a bunch of times and taking a whole series of snapshots, they've proved that they do in fact have a working quantum computer.
At the moment, the D-Wave One can't do much else besides these extremely specialized problems, but since it's designed to operate as part of a more conventional computer system, there's some hope that it'll eventually be put to use figuring out the question to the answer of the question of life, the universe, and everything, while also helping you crack the DRM on all your pirated movies.