Nintendo's first smartphone app, Miitomo, launched with a lot of fanfare. But how many people are actually interested in it? Quite a few, if you ask SurveyMonkey. It estimates that Miitomo has racked up 4 million people who use it at least once a month, and 1 million who use it every day. Supposedly, that translates to about $280,000 in in-app purchases every week. That's not a huge amount of cash in the context of Nintendo's console games, but pretty healthy for a brand new (and relatively niche) social network.