I just finished reading Peter Thiel's notes from his Startup class and he suggests almost all businesses are in fact monopolies, yet pretend not to be by competing in other environments. Google has a monopoly on search, FB a monopoly on social networking, etc. I don't know if I agree that either of them are complete monopolies, but the moat is certainly thick. In a perfect business world, shouldn't those be broken up if they are in fact monopolies?
There's nothing wrong with being a monopoly in the sense that you simply won by having the best product. Where monopolies needs tempering is when they use their power in one market to displace competitors in another market - such as Google accused of doing by giving prominence to search results from their own properties over competing ones.