I downloaded the app in a few seconds (from the iTunes store), and fired it up. There was no configuration required. When it started up, I aimed my iPhone at the local horizon and got an image (through the iPhone's camera) much like the one at right (click to enlarge).
What you're seeing there is a realtime video display of whatever your smartphone is looking at, but the mountain peaks are overlaid with a little symbol and an annotation giving you the peak's name and altitude.
I live in a fairly obscure valley (Lawson Valley) in the foothills of the coastal range in San Diego County. The “peaks” immediately around me are really just the tops of slightly larger-than-average hills; all of them are less than 3,000' high. Peak.AR knew the names and altitudes of every one of them – even several local peaks whose names I've never been able to find, not even on Geodetic Survey maps. Peak.AR must have access to an amazingly large database of peaks!
Highly recommended, a 10 on the awesomometer. Their home page is here.
