We changed it six months ago- once we were able to afford the design talent to make a good go of it.
http://cl.ly/3O3H300K3C3p423G2i2Z
It's another bookshelf icon, but the colors and style make it stand out in the app store listings.
Key is to stand out relative to competition, in the common ways users find your app.
Downloads and sales have more than doubled since the change, though we also redesigned the app interface itself in the same update.