If you ever look at the night skies and try to identify anything other than the moon then Planetarium 2.0 ( http://www.aho.ch/pilotplanets/) is alone worth buying a palm!!
This is one of the best Star Atlas I have seen and it is really fast. Attention to small details like a “night mode” where everything is drawn in red against a black background shows that a lot of attention has been paid while programming. Also most of the actions dont take more than 2 taps of the stylus.
Last but not the least it is very reasonably priced at $24 as compared to $100+ for similar software on PC which is no good anyways cause it is a pain to have a laptop around while you lie supine on the terrace – yeah thats my fav for watching the skies, and not to mention I dont have a laptop!!