Looks like MS will use this as the basis for the next version of Office with it's Office Web Apps.
Source: http://arstechnica.com/microsoft/news/2009/08/microsoft-buys-officecom-domain.ars
ArsTechnica said:On Tuesday, Microsoft acquired the domain Office.com. Microsoft likely paid a pretty penny for the valuable domain name. Some may find it surprising that the software giant didn't already own it, but it's true: it previously belonged to a US resident and was operated by ContactOffice, a Belgian startup that markets virtual office solutions under a revenue-share agreement. The transfer, however, isn't yet complete.
Source: http://arstechnica.com/microsoft/news/2009/08/microsoft-buys-officecom-domain.ars