In reply to redscotti:
I'll confess that a large portion of my appreciation for PeakFinder is that it's a very nice app in terms of the interface etc - it's enjoyable to use and share with others on a hill/mountain/crag day. I was lucky to buy it ages ago when it was a fraction of its current price.
In terms of accuracy I've not encountered any problems - but haven't rigorously investigated. Sometimes the view isn't perfect in terms of nearby features (like the shoulder of the slope you're on and the local horizon it forms). Overall however I've found it very impressive - especially for a surprisingly small downloaded dataset. I suspect the actual peak identification is very accurate (being the easiest bit in terms of coding).
Like kinley2, I've found the sun/moon tracks with rise and set times very useful. A good number of times I've used it to check when the sun will reach/leave a hillside crag. Though I normally do that on my laptop using the website - which I believe is free and includes most of the features of the app (less the 'live' display that tracks where the phone is pointed).