Well, as has been pointed out[0] on Scott Aaronson's blog, it wouldn't be so hard to tell if, say, you had a universal quantum computer; you could run Shor's al

Well, as has been pointed out[0] on Scott Aaronson's blog, it wouldn't be so hard to tell if, say, you had a universal quantum computer; you could run Shor's algorithm, quickly factor some large numbers, and have a pretty convincing demonstration. The D-Wave machine is more limited, however; it only does quantum annealing, and the thing about quantum annealing is that it gracefully degrades into classical annealing. This is a plus if you want something that will work when your qubits are low-quality (such as in the case of a D-Wave machine), but a minus if you want it to be unambiguously quantum. Edit: In addition, apparently it's not even clear how much of a speedup quantum annealing provides over classical annealing in the first place, which is a sort of just a general minus. [0]http://www.scottaaronson.com/blog/?p=1687#comment-100732 http://www.scottaaronson.com/blog/?p=1687#comment-100732