Augmented reality will be truly useful when it can discretely tell us the names of the people we talk to at press events and so help avoid exposing our awful memories, but until then we'll make do with knowing what planes are in the sky. Plane Finder AR - for the iPhone 3GS and iPhone 4 - is a $2.99 app that promises to identify which aircraft are overhead and label them in real-time using the Apple smartphone's camera.
The app apparently uses ADS-B plane feeds which commercial flights use to transmit their name, position, destination and other information. Unfortunately, that also means that if the plane isn't using ADS-B (apparently US airlines have been "slow to adopt the technology") then it won't be labeled, and indeed some of the reviews on iTunes are less than positive. Still, if you're willing to give it a try - and we do like the concept - you can download it here [iTunes link].