D-Wave's advancements are very interesting to me for a few reasons. The first is that initially many people suspected D-Wave was a scam, because the most successful research efforts in quantum computing used just a few qubits, and D-Wave claimed a massive improvement (something like 128 or 256). Scott Aaronson (http://www.scottaaronson.com) was perhaps the most vocal critic. Over the years, the criticism has softened, and D-Wave has managed to get a paper or two into Nature. I think the truth of what they've achieved is somewhat less than what their marketing machine would like to suggest, but it's nevertheless very impressive (and D-Wave is certainly a place I'd like to work at if I could).

To clarify, D-Wave has not developed a general-purpose quantum computer, and in fact the term "general purpose" is kind of ill-defined for quantum computing anyway. Right now, there are a lot of different quantum effects that are used in different ways to accomplish specific tasks. I believe D-Wave's device uses quantum annealing to solve certain optimization problems, but someone check me if I'm wrong.

The little I do know about quantum computing relates to my area of study: simulation. The computation required to exactly solve the Schrodinger equation scales with 2^N for the number of particles (or whatever basis the equation is set in). Even the largest supercomputers are incapable of doing more than a few atoms [which, incidentally, is actually what I'm attempting to accomplish right now for a project that I should be working on instead of posting on here...] Anyway, with quantum computers, the scale would be O(N) instead of O(2^N), so you could perform incredibly accurate simulations that reach chemical accuracy. Chemical accuracy is kind of the holy grail of simulation, because what it means is that you can predict actual, macroscopic chemical properties of a variety of substances without doing any real-world experiments whatsoever. I believe it has been accomplished for things like pure hydrogen and quite a few bosonic systems (bosons are easier to simulate since they don't suffer from the fermion sign problem - http://en.wikipedia.org/wiki/Numerical_sign_problem).

Anyway, I probably sound like I know more than I really do, but hopefully this gives you an idea of what kind of applications a real, working quantum computer could be used to achieve.