Pages is great, as long as you have a Mac with Pages to do the final formatting. Standalone ... maybe not.
Frankly, you're better off writing in plain ASCII in something like Compositions or PlainText, then picking up the text file from DropBox when you get home and do the layout on a real computer. I love my iPad and I'm amazed at what they've managed to achieve with Pages for iOS, but it really is like trying to shoot an elephant with a pellet gun. If I did more presentations I would buy Keynote for iOS just to present but the actual presentation I would create on Keynote for Mac. I'm not a spreadsheet guy, so I won't comment on that.
As for doing serious productivity work on an iPhone, don't be silly, it's a phone, after all. If you buy a package for the iPad and it is universal, you might as well load it on the phone as well, but that is for quick reference to your docs, not for actual data entry.
