[nicw]

Skipping the first note, the author makes a strong point about keeping it simple. You may have an amazing idea, but if the user can't jump in, perform <x> and then jump back out, it's not likely to catch on.

By only having one thing (add text to photos), you're really letting the users vote about whether they would use that functionality. Try to pack too much into your first version of an amazing idea, and you'll have a tough time parsing out which needs tweaking when you're not getting traction.