I don't care for Facebook, and it certainly wasn't the first of its kind, but I still have to give Zuckerberg some credit. Whatever it was that he did differently for Facebook than was done for previous social networks, it worked, and it has reached the general public in a way that few other technologies have.
Furthermore, I don't know of anything particularly immoral or unethical that he has done with his position, and he has donated and pledged quite a bit more of his money to charity and schools than most people of similar wealth.
There are definitely many others who are deserving of this title, but I see no issue with Zuckerberg winning it for this year.