You could make an argument that one of the things holding back the growth of location-based service Gowalla was that there was no full API support. After all, rival Foursquare has had their full API rocking and rolling since last November . But after today, you won't be able to make that argument anymore. Gowalla has just formally announced that their Check-In API is now available to all developers. This is an extension of the API Gowalla released this past February. Notably, that API was read-only -- but today's addition brings full write capabilities to the Gowalla ecosystem as well.