Funny enough. I also use the iPad for the same stuff some musicians posted earlier. Though for me, the top of my list is stuff like iBooks and Good reader. I tend to use my iPad on music stands instead of having to keep a bunch of loose papers with music on them. It's a whole lot less error-prone and much easier to handle. Not to mention, you can have a ton of music sheets captured on the iPad where stacks of papers quickly get unwieldy. However, the fact that you can turn pages without error and without worry of dropping sheets, is a godsend.
This works out because well, the iPad is the right size, and it can rest on a music stand unlike a laptop. I also keep music previewed on it as well. Due to a bi of multi-tasking, you can keep listening to stuff you need to practice while reviewing the written stuff, and or set lists. There's so many ways to cheat and review with this combination.
Also, in a surprising way, I also often depend on Pages and Numbers on it. Perhaps it's because I've already put in some documents which get frequent updates. And the ability to one button export them for review is very nifty since I do share those documents.