I have the iWork apps on my iPad (and before that I relied on documents to go).
I rarely create new documents on my iPad, but I do a lot of editing, proof reading, and finalisation of documents that I then share, send on, present, etc. I consider myself highly productive on my iPad - even though I still have a notebook at my desk on which I will knock together complex presentations or spreadsheets, before iCloud syncs them onto my iPad where I will continue working on them or present them from using key note or numbers. In a typical day I spend about an hour or two in front of my notebook at my desk; and the rest of the day is spent on my iPad in meetings, workshops, waiting rooms, aeroplanes, etc.
I doubt that having Microsoft Office for the iPad will change the way I work, much. I suspect that there will be less fixing and tiding up of PowerPoint or Word documents that Keynote or Pages mangled during the conversion process. But I will still spend more than half my time on the iPad reading, editing, changing, commenting on spreadsheets, presentations and documents in collaboration with others and am unlikely to change the volume of material authored from scratch on the iPad itself just because I now have Office for the iPad.