Sheet Music App

I'm getting to the point now where I'm taping sheet music pages across my Yamaha U3 - and that's not going to be sustainable in the long term (unless I buy one of those pianos with > 88 keys :-)

I see Ben and various other people use what looks like an iPad - once you start on longer pieces, is a larger format iPad with an app what folks use? I'm curious to know what folks use app-wise

Thanks!
Tim from New Zealand