Tele-Read reports that iBooks has taken a tumble; it's no longer the most-downloaded app for the iPad.

Apple’s iBooks Store has just fallen from the top rung among free iPad Apps in Apple’s Top Charts listing...iBooks has fallen to #2, and the Kindle Store has climbed from the mid-20s to #13 in recent days.

It's probably smartest for Amazon to treat the Kindle like a system that can be used on many devices. The e-ink reader, sooner or later, is going to become a dated technology that seems ridiculous in retrospect. But if the Kindle app manages to supplant iBooks on the only device that can actually use iBooks, that would be a huge coup for Amazon.