This summer, my orchestra took a risk. Yorkshire Young Sinfonia became the first youth orchestra in the world to become 100% digital, using iPads and an app called Newzik instead of sheet music.
Cool story. Interesting that they are using Newzik and not something like forScore. Newzik is a really cool alternative but I personally do not have a huge need for reading XML files on my iPad. Most of the scores I work with are scanned copies of original paper. There are a lot of cool things you can do with XML though, like resizing the music and having the entire layout of the score adjust itself to the size you prefer. Neat stuff.