The app provides a quick and simple way to get your altitude. I have never had a chance to check the info against an authoritative source, but the results that I get using the program seem to jive with the other info I have. My only gripe -- a small, small thing -- is that I have yet to see a way to set the app to report in feet, rather than meters, as soon as I open the app.
Twigs in Omaha about Altimeter X