I wasn't aware that many phones other than my Galaxy Nexus S (Google version) even had a pressure sensor. It's main value for me has been knee pain prediction; that and watching the pressure drop with the approach of hurricane Lee last year.
As for indoor navigation, I can see the phone integrating the accelerometer output, but that assumes an accurate position fix before going inside a building, with good GPS signals and data connection to a network. I'm one who keeps the GPS turned off mostly for battery life, but also for personal privacy. However, I'd pay for an app that could navigate me to items in a grocery store!