A video for the Technical Preview of Microsoft Office 15 has leaked onto the web explains how you can use your Windows LIVE ID to sync files across your PC's.
This video is played on the first run of Office 15 after completing installation explains how logging in with a Windows LIVE ID can help sync your files across your computers with the cloud.
Since Office 15 is heavily integrated with the cloud, it will be personalized with the login you use.
Also, the coming Office 15 client apps all seem to be getting a new "touch mode" button that will enable them to work better on touch-centric devices. Microsoft officials already shared that the four Office 15 apps that will be "included" on Windows 8 on ARM (WOA) tablets will be Desktop apps, not WinRT-based Metro-Style apps. So how will Microsoft make these versions of Word, Excel, PowerPoint and OneNote work better with touch than their current-generation counterparts? It seems that Microsoft is including a button in each of its Office 15 apps that enables a "touch mode."
This image of the technical preview version of Word 15 -- shows off that button: