Have you used Office 2007 yet? It's quite a bit different from Office 2000 and 2003, but, in my opinion, it's a pretty spectacular leap forward. This has been well-document elsewhere, but is quite a shift that the blogosphere can't quite capture as well as first-hand use. It is, in fact, enough of a leap forward that I don't believe OpenOffice, as an Office 200x clone, can compete. OpenOffice is a great product, is free, and seamlessly cross-platform. However, the biggest reason I'm continuing to use Vista right now instead of the latest Ubuntu distro I just installed is Office 2007.
This is not to say that OpenOffice is inferior or in any way bad before the flames start flying. However, my users (mostly students with Office 2007) have very quickly adapted to the interface, feel that it is intuitive and flexible, and like the tight integration of all of the components. Here in public education, we get such substantial discounts on Microsoft licensing that cost is somewhat less of an issue than it might be as well. Full blown Office 2007 retail would be utterly unobtainable here, but educational pricing is such that the free factor of OpenOffice doesn't give it the win by default.
OpenOffice's greatest assett (aside from being free) is the easy compatibility between Linux, Windows, and Mac platforms (no conversion necessary). While such is not the case for Office, we're in a pretty homogeneous environment here, so the cross-platform usability is less of a selling point.
Tabs, pivot tables, and a slick new interface? Is it worth it? A lot of my students think so. A lot of my older teachers disagree and miss the OpenOffice/Office 2k interface.
So what's the verdict? I find myself still using Vista much more than Ubuntu (even though so far I find that I prefer Ubuntu and it's abundant free software, easy networking, and snappy performance) because I've become so enamored of Office 2007. I think I need to spend some more time with OpenOffice and see if I can end my illicit affair, for fear of being labeled a fanboy. Office 2007 is a hard habit to break, though. I'll keep you posted.