I haven't noticed anyone else mention using an iPhone as an observing aid, however I have been using mine when observing in the upper mountains in the past few weeks.
A while ago I was using Starmap (the basic version) but now StarmapPro has been released - and its a whole different ballgame, basically all the features of a desktop app like Starry Night, a massive catalog of faint objects, and a user interface that is quite easy to use.
Basically StarmapPro is indispensable. My old atlases never got a glance and over the weekend I'm going to add an iPhone cradle on the scope.
http://www.star-map.fr/
Even on a desktop/laptop you be hard pressed to find a better astronomy app - let alone one that fits in your pocket and knows the time, where you are and which way is up.
Now all it needs is a bluetooth interface to control the scope and a camera and it would be way better than Vixen's StarBook.