I guess we haven't made this clear enough and that's our fault, but we charge upfront for the app and a year's worth of service. After that, it's $4.99 a year. We're not sure that this is the best business model (when compared to Evernote's for example), but we do know that we will not sell data or advertise. With this model, each paid user covers the cost of their usage (and not the usage of the 10s of free users their money has to cover with a freemium service) and it means we're still incentivised to continue to update and improve the service, so people renew their subscription at the end of the year.