Carl and Richard talk to Rob Irving and Simon Jackson about advertising on mobile apps. The conversation starts out with Ad Duplex, which is an ad exchange and a way to advertise your mobile app on other mobile apps like yours - all in an effort to get more users. Rob talks about alternative ways to get users, such as pursuing reviews, using crowdsouring and in general taking marketing seriously. Simon digs into more traditional advertising using the open source Adrotator library, which takes the discussion into the complexity of advertising - multiple providers, different systems for different locations, and how often you don't actually *get* an ad!