That's about 4 photos per user. Doesn't seem like a lot. How many of your users have over 100 photos, 200, 300? Those are the ones you want to concentrate on.

That's about 4 photos per user. Doesn't seem like a lot. How many of your users have over 100 photos, 200, 300? Those are the ones you want to concentrate on. Ask them how to make the service better. They are your power users. Most everyone else is just a lurker.