I've got to start off by saying that I'm an Apple fanatic, and therefore have a general hatred towards anything branded with the Microsoft logo... but they have really excelled themselves with Office 2008.
Having purchased iWork '08, I was disappointed by the lack of ability to save natively in the most popular formats (.doc/.docx), you have to go through a process of exporting the documents and they aren't always reproduced as they were saved, etc.
So initially I decided to go with Office 2004, which granted, was good, because it was simplistic.
But since then I have upgraded to Office 2008 and what a difference! Making documents look professional has never been easier. Recently I have been making a lot of flow diagrams integrated within my work and its unbelievably easy.
Absolutely amazing product, and great value!