The onscreen keyboard is a real weak spot for Windows 8. One flaw is that the onscreen keyboard isn't always smart enough to pop up and go away automatically, such as when you double-tap in an Excel cell to edit text or single-tap in a cell to format it. iOS and Android are smart enough to do so. Windows 8 -- especially the Windows 7 portion -- is also not smart enough to move the screen focus so that the active element is not covered by the onscreen keyboard, as iOS and to a great extent Android are. Nor does the keyboard adjust to the contents to present the most likely useful keys, a hallmark of Apple's iWork for iPad. It's stuff like this that shows Microsoft's superficial integration of touch into the traditional Windows 7 Desktop. Plan on getting a Bluetooth or other keyboard for prolonged use at a desk.
The more I used Office, the more rough edges I found, which I hope reflect its beta status more than anything. For example, the pinch and expand gestures to zoom in and out of documents don't always work. When you enter full-screen mode, there's a nice control to get your ribbon bar back temporarily -- problem is, as soon as you tap anything it disappears, turning this convenience into a frustration. Document windows don't always resize to fit your screen dimensions, nor move their focus to accommodate documents wider than your screen.
On the other hand, you get the comprehensive set of Office capabilities. Yes, Office has way more features than anyone uses, but there are none of the compromises that you get with iWork on iOS, Quickoffice on Android and iOS, Documents to Go on Android and iOS, and Office2 HD on iOS -- the last of which is the sole option if you want revisions tracking for Word documents while editing on the tablet, for example. iWork's Keynote is a formidable presentation app, better than PowerPoint, and the spreadsheet function in Quickoffice is very capable as long as you don't use linked workbooks or specialty formulas.
But at some point when working in iOS or Android, you'll miss Microsoft Office. Yes, the Office cloud service CloudOn lets you run Office 2010 in a fairly optimized way on iOS and Android, but the interface is a bit scrunched and you must have a live Internet connection.
If only it weren't Office for Windows 8I can see Office 2013 being a major reason for people to want a Windows 8 tablet -- too bad that the only tablet it runs on will be a Windows 8 one. At this point, I can see it being usable only on an ARM-based Windows tablet, the one without the legacy Windows 7 Desktop to get in the way.