The completely new interface in Office 2007 is shocking to say the least. A ubiquitous software like Office thrives on the fact that practically everyone knows how to use it. The dramatically new interface no matter how good is bound to scare the low skilled user and the power users are likely to stay with what they are already comfortable. All the Office file formats have an "i" at the end. Its now ".doci" instead of "doc". There are bound to be other such compatibility issues once you delve deeper.
As for Vista there are enough signs that its Mac-like OS, but a few years late. Coupled with the need for more high-powered hardware, a Vista upgrade makes little sense. MS is really starting to sound and act like IBM of the past!