Between Kindle and iBooks, I prefer Kindle because of the greater science and math selection and the generally lower prices. I use Kindle on iPhone, iPad and Mac desktop with no problems at all.

This app was working perfectly for me until I noticed today there were "sponsored" ads in ALL of my subscribed feeds! No thanks, guys. I paid the extortion fee to get them out of my face this time but I'm now looking for an rss reader that doesn't shove ads into my feeds. There's no such thing as an unobtrusive ad.

I'm sitting in the Hickory, NC store and the store's Hot Now light came in about five minutes ago and the app didn't alert me. Notifications are enabled.

This app has worked flawlessly for me on both iPhone and iPad. It's great for planning upcoming observing events and for describing events to the public.

The only thing missing from the iPhone version, compared to the iPad version, is each element's spectrum. Other than that, it's essentially perfect. I recommend it to my students (I teach astronomy and physics) as the iPhone periodic table app of choice.