The current Microsoft Office and OpenOffice.org work in a roughly similar way. But the new Microsoft Office 2007 is essentially a whole new program, according to many reviewers including David Pogue. So when you're thinking about switching to Microsoft Office 2007, don't just think about the price -- think about the retraining effort.
So why upgrade to MS Office 2007? Pay nothing, and switch to OpenOffice.org, instead. You retrain for both, but the cost of OpenOffice.org is hundreds, thousands, hundreds of thousands, or perhaps millions of dollars less than Microsoft Office, depending on how big your organization is. Saving a lot of money is, well, really good. It lets you spend that money on something that's actually important: education, cure for cancer, better pizza, or whatever your business or organization is about.
Here's my extended-dance-version blog post on this.