Ars reviews MS Office's touch functionality - it seems Office has a long way to go.
from their conclusion:
As a set of reader applications, the suite works tolerably well. Opening and scrolling through documents works, and because these are the full Office programs, files are displayed with full fidelity and functionality. However, in this context, I find it hard to understand why Microsoft made the effort it has; Even Office 2010 works adequately well for just reading documents on a touch PC.
Unfortunately, as soon as one ventures beyond mere reading, the experience becomes unsatisfactory. Finger users attempting to make edits will find themselves regularly dumped into interfaces simply not designed for imprecise input, and even if they stick to the "main" user interface (the ribbon and pop-up toolbars), that interface works poorly. The interactions with the on-screen keyboard are frustrating and the interface is cluttered, leaving too little of the working area actually visible.
Having the real Office applications and their perfect support for Office documents is valuable—but this needs to be married to simpler interfaces that are engineered around reading and light editing, and that remove entire features and user interfaces that are too complex for finger usage.
As things stand, far from being a valuable feature of Windows RT, the Office 2013 applications threaten to make it worse.