I own Keynote and Pages for iOS and I use them mostly for school related things such as taking notes, writing mid-to-short essays, and viewing/making presentations while I am in class or studying.
I mainly use them on my iPad and I'm going to be honest, even though there are drawbacks compared to desktop software, iWork for iOS is one of the most powerful (if not) mobile production suites out there. They are very feature packed and snappy and if you're looking for an above basic set of tools for this, iWork will be your best bet.
There are some annoyances, though, like list creation has been (and still is) a pain in the ass, especially when creating lots of indents and unindenting due to the fact that you have to access a popover and often change the tab to begin modifying the structure. Same goes for changing font styles, you have to access a popover to change the settings. An additional few steps in the process, but I would happily take the trade off.
I have yet to really "use" them for the iPhone, though. I mainly open docs on my iPhone to view them for a second or pick something out of my notes whenever I am away from my computer or iPad so I can't give you much insight on the smaller screen controls.