I'm not entirely sure just what I'm thinking right now. What I've got is yet another app like Pierogi, carrying with it a small dense database of info. The source code is simple (and I see no problem with releasing it open-source), but the database is going to take a lot of effort to create and maintain. (And yeah, I don't expect I could live off selling apps to the Maemo community alone. I'll also be trying to squeeze this app into the iOS and Android worlds.)

As Estel noted, in today's world it's just about as easy to distribute a "cracked" closed-source app as it is to distribute a modified open-source app, so there's probably no real security advantage to closing certain modules in the app.

So, I can see both having a sample database for people to first play with the app, and an activation code to enable the whole database; or simply an activation code for the whole app. (Or, if nothing else, just the standard request for donations...) In any case, I don't see how I could stop folks from just tinkering with the app to bypass the payment system, so asking folks to act honorably would probably be the best deal...