iPhone app that shows app usage statistics?
Cydia's App Stat does exactly what you've requested. As far as I can tell, it exists since April 1st:


  New Tweak in Cydia, App Stat, shows you your app usage statistics, frequecy of use, use of time and recent use. Supports IPhone, IPod Touch, IPad running IOS 3.2 or later. Free on Cydia Search for it.