Now if only you were permitted to write software to take advantage of the cool hardware you build.
Also worth noting that square is not drawing power, doing so might make them reject your app. Especially because this harvest method is fairly inefficient (power is being converted twice before its useful). Draw on the iphone battery may be 4x the power used.
Among them is a laser pointer [1], a controller for RC power outlets [2] and countless others.
[1] http://hmb-tec.de/iPhoneApps/LaserPointer.html
[2] http://www.hmb-tec.de/HMB-TEC/Funksteckdose.html
(Links are in German)