Localytics, InMobi and others firms are trumpeting the importance of "customer lifetime value," which many others dub "lifetime value of a customer" (LTV), to app developers. It's not a simple metric to grasp, but as the app industry matures, expect to hear a lot more about LTV, according to the firms. Most LTV thinking is based on how much revenue is coming from individual customers. This could be money generated through paid downloads, but also includes in-app purchases. Then developers must cross-reference that with any kind of promotional activity they are doing for their apps, including ad campaigns. Experts say developers should also think about the other, arguably most popular way apps find an audience: through word of mouth or social referrals. If customers are actively talking about an app on Facebook or Twitter, their LTV immediately goes up. To find out more about the calculations, check out this FierceDeveloper special report.