Most people tend to agree that it is not good to have NO competitors. I believe this is primarily when you're starting out. You're trying to decide if there's

Most people tend to agree that it is not good to have NO competitors. I believe this is primarily when you're starting out. You're trying to decide if there's a market at all and having competitors lends some credence to that. Once you already have the traffic that FourSquare does, I don't think it matters anymore. One case where it might be different is if there were some paradigm shift where there were a whole bunch of similar companies for a long time and all of them had dropped out of a dying game while a single company was holding on -- but that's not going on here.