It turns out that the next iteration of Microsoft Office, Office 15, will actually have a dedicated WOA tablets version, making one of the big question marks before the success of those slates pretty much a moot point. Moreover, the whole interface will be touch-optimized, not only meant for a mouse, and Office 15 will be geared towards low power consumption, which is the main point of ARM-based tablets.
The UI actually looks more like the Explorer one, than that of the typical Metro apps, which is explicable, since Office is a pretty powerful tool and demands a more sophisticated interface. Full-blown Word, Excel, PowerPoint and OneNote are all in store once WOA hits sometime in Q3 or Q4, and all file types that are supported on x86 machines you can work with on ARMed Windows 8 slates as well. Here's what Microsoft's Steven Sinofsky had to say about the exciting news: