If the iPhone has a leading app genre, aside from gaming, I'd say the current surge of "check-in" apps is probably it. Sure, back when the App Store first opened up, Twitter apps were everywhere (and they're still being made daily, it seems), but in terms of a genre that can only exist on a location-aware device like the iPhone, "check-in" apps like Foursquare, Gowalla, and so on, are making their mark right now. Here's news on two such apps continuing to grow on the App Store skyline.
First up, Loopt [iTunes link] has announced a partnership with a company called Mobile Spinach to start trying to monetize this kind of app usage. Mobile Spinach delivers local ads, and Loopt says that it'll be using their location-based social networking service to bring specials and deals to users from wherever they check-in from. Note that while Apple doesn't necessarily want location-based advertising as the sole purpose of an app, it seems to be all right with location-based advertising as an extra feature like this. Loopt tells us at TUAW that it's a great deal for the company, as it is "an easier and cost-effective way to do online/mobile advertising," and that it means "Loopt users can get great free offers on everyday things they want in need just by walking around in the neighborhood." It'll be interesting to see just how useful this extra advertising can be.
After the link below, read about how MyTown finally got the success they'd been hoping for.