I still like Office 2003 because it is almost just like Office 2000, and I did not have to re-learn how to use it. Office 2007 works the same in many ways, but has a very different look and anything that I am used to using on the toolbar seems to me to be in a different place and I have to hunt for it.
That said, my son loves Office 2007. One feature that he showed me, that I have to admit is great for a student, is that it will now format footnotes and works cited using any of a number of standard methods, such as MLA. However, I have not found much use for that in my practice. There may be other upgrades that I am not aware of because I am still sticking with my 2003 until I upgrade computers.