I have used my ipad to show chord charts for a conference I attended last year. My good friend Ben Juster (inactive member here) uses a program in his congregation called OnSong. So for the team he put together, he sent us all OnSong files for the music. He uses a bluetooth foot switch to change pages but I have not used OnSong enough other than the conference to warrant the expense of the foot switch.
Beyond that, a couple of years ago I broke my left arm and could not play bass for about 2 months. So I used the bass in GarageBand and played it with my right hand. My wife could tell the difference but she may have been the only one.
I really love the app "Anytune".
I use it lots for practicing songs we do at our church because I can take a song (that I have downloaded to my IPad) and put it in different keys, do loops etc.
It has made practicing so much more enjoyable and productive.