Not all iPad owners/users are business-oriented -- as a working musician/music-teacher/conductor I find that the iPad app I use every day for long periods of time is forScore. Loaded into this app I have placed well over 500 full orchestra scores, the trumpet parts for those same orchestral works, my parts for a brass quintet I perform with, most of my personal trumpet music and recorder music library and I'm constantly adding to it. forScore is an incredibly robust app that serves me as an electronic music stand and allows me to carry a huge music library with me all the time -- if I had the printed music with me I'd need a van with bookshelves to hold it all!