Everything I said about Windows XP goes double for Office XP. Microsoft's Office Suite delivered everything you'll ever need in a word processor, spreadsheet, database and so on several versions ago. Microsoft just needs a little revenue bump every now and then--which it has every right to seek.
But you should have the right not to open your wallet until you're ready. Without going into detail, the single most innovative feature of Office XP is the way it forces you to buy more copies more often. Its other features are incredibly granular, which makes a weak cover story for that strategic goal. Your productivity gains are not very likely to completely cover your deployment and support costs.
But that's not always true of new releases. There are various reasons for frequently upgrading security, tax, multimedia, Web and communication programs. For example, right now, some college kid is out there creating an innovative little piece of code that will add one more wrinkle to the rapidly growing blob of viruses that threaten your PC.
But desktop productivity software? In most markets, the only real competitive threats to Microsoft's new software versions are its old software versions. Still, more than half of Microsoft's customers are choosing not to use the latest Office version because they don't want to give up familiar features and because upgrading can be a real hassle.
Recommendation: If it ain't broke, don't fix it--that is, until Microsoft makes you.