I have been asking that question since I got iPad 2 shortly after it was introduced. I am still asking that same question. That quite much sums up the situation. Not an easy task for few reasons.
First of all, I use (or I am actually almost forced to use) PC at work. Not a Mac (which I use at home). I write scientific articles, funding applications, and many other kind of documents using Microsoft Word because it is most widely used word processing system and it actually has the best document commenting and tracking system available. So this info is important as a background.
I would like to use my iPad in many meetings we have here at work to make notes and short memos which I could easily transfer to my PC and which I could effortlessly distribute to my colleagues. I have tried so many kind of note making apps with iPad and no one of those have been great. Sometimes I would like to open a scientific manuscript with my iPad and make some corrections in it. Not an easy task. Actually I find it quite much an impossible task. It seems that an iOS version of MS Word would be needed to effectively work in this PC-Mac-iOS world.
I think the easiest way to fix these problems would be to buy a MacBook Air and istall MS Word for Mac in it. Then I would have the best possible (even though not perfect) solution for my above problem. But that solution would cost me about 1000 euros in minimum.