I've been a happy user of FourSquare for more than three years and I've logged 1225 check-ins in this time. Especially, when Šam was still with us, it was great competing with him for mayorships of our favorite places such as Pomf. But after checking-in for 500th time at Zemanta, I've asked myself why should I keep on using FourSquare and, since I couldn't find any good reason, I've stopped checking in altogether. I might miss to know some statistical facts about my life, but for now I'm perfectly happy that I'm not quantifying my every step (and I gladly let NSA do it for me). While talking about successful start-ups exponential user growth is still hallmark of success. But in reality user retention is much more important metric than user acquisition. If your service is used only due to a hype, without delivering any real value to the users, no amount of virality will enable you to build a sustainable business. The best what you can hope for is to earn some quick and easy buck, which seems to be a prevalent fortune especially for mobile applications. But if you want to create a truly repeatable business, you must strive to understand the value you deliver and work hard to deliver even more of it for your users. Otherwise you'll end up with an empty space and bitter memories of past success.