Just got my iPad today... and the CourseNotes app is amazing! PERFECT for school this coming fall 
Tried once, too bulky ... Still prefer the IP4 for that purpose... Bathroom reading material.
I host a Django Reinhardt/Hot Club of France jam.
We frequently have guest singers so the ability to transpose on the spot is great.
There are hundreds of pre-charted tunes on the iReal book website.
You can also download the crude software and make your own charts. Once they are on your iPad you can arrange them in Songlists. Once you are onstage you can stay within the Songlist and swipe left and right for the other songs in your set list. Very quick.
There are dedicated ipad Mic stand holders being developed and bluetooth footcontroled page turners.
There is a certain redundancy with the iPad. Just the fact you need a computer with iTunes to get started speaks volumes. But this is why I started this thread. It's not necessarily some earth-shattering new app, often it's simply the elegant and thorough repurposing or re-implementaion of a product or idea that combine with the iPads' inherent strengths and voila game-changer.
For me, iReal book is that app.
I encourage you to check it out.
Went on a week long jazz course in Trinity College, London. used my iPad, and probably sold about a dozen!
Used iRealbooks, as did many others but via iPhone. The iPads screen made it much easier.
Used Goodreader to view PDF scores, of jazz lead sheets, it's an ideal size for that, prob not big enough for orchestral scores, but fine for lead sheets.
It replaces a stack of manuscripts that would otherwise need a suitcase to transport them.
I used iAnnotate PDF to add, er, annotations, although It would be so much more convenient if they could share a file system.....
Used sound paper to take notes during seminars, and record samples of playing.
Used my iTunes library to buy, and play relevant music as we were discussing it.
Used spotifly to find music quickly to play to the others. Was v useful, someone might mention a tune, and it's relation to another, and I could quickly play several versions of it..
Used Shazam to quickly identify and analyse music that tutors put on the PA
Used polytuner to quickly and accurately tune my guitar
Used my iPhone camera with a photocopy app to copy and enhance music, send to drop box, and open in goodreader.
Used omnifocus to collate what I'd learned and formulate a practice plan
Used safari to get to wikipedia to research musicians etc..
Was incredibly useful, and people who before saw the iPad as a toy could see it's usefulness- size if screen, battery life, and portability. With a apple case, sat very happily on my music stand, adjacent to the music.
A superb piece of kit for a musician.
Went on a week long jazz course in Trinity College, London. used my iPad, and probably sold about a dozen!
TakeNotes.
A simple app that let's you mark up PDFs and other documents. Highlight, scribble, add text notes, etc.
I'm a director/choreographer and being able to make notations on scripts and scores, diagrams for traffic patterns in choreography, etc., has let me carry one device instead of several several books and notebooks.
Walking around and easily sharing photos and video with prop, costume and set departments doesn't suck either. Make that my MacBook that I don't have lug around anymore either.
drmacjazz said:then when the lights get dimmed they "get it" even more!
Air Video. I have all of my DVDs and tv shows ripped to a hard drive on ny server. Hense, i have a little over 2 terabytes of video available on my iPad even when i am not at home. (3G)
I'm a jazz guitarist. I host a weekly jazz jam. The app iRealBook completely justifies owning the iPad for me. I've used my iPad for my last 3 jams/gigs and it works great. The wonderful thing about iRealBook is it's ability to transpose the chord charts into other keys INSTANTANEOUSLY!!!
All the other apps, games, books, videos, etc are just gravy for me. If they never upgrade the ipad or create any new apps, i'd still be happy. I used to lug a 10lb binder and the charts were static of course, no instantaneous transposing.
Any other apps that are this much of a game changer? Surely symphony orchestras will be moving en masse to the ipad?
Email and Safari for starters.
I'll +1 that! Apps are great, but I bought the device for web browsing and email.