iOS 5 will supposedly make it dead easy: iWork Apps (Pages, Keynote, Numbers) sync transparently between your Macs and iPad/iPhone, or at least, that is the plan
We'll see how well they do it.
Pages is a decent word processor-but I feel it is more of a glorified text editor than a full processor like Word. Keynote is much nicer (imho) than Powerpoint. Not that impressed with Numbers to tell the truth-but maybe I have been too Excel-centric over the years and just can't make the transition.
Never had much trouble with compatibility file wise-but the Office Docs we use at work (on Windows) aren't really that complex. Plus, we have moved to Libre Office from Microsoft Office. Our Mac guys are trying Libre Office as well, just to keep things simple. Not sure if we'll transition them to iWork (they use iWork at home on their Macs I think)