I still use Office 2000 and I've no need to upgrade. Why you ask?
O2K's wonky in a few places but with sp3 it's reasonably reliable and stable.
Why would I bother changing as nothing much has changed in 12 years that I would use? Moreover, there's been no change to the grammar checker, little to the speller and negligible changes to page formatting, headers and footers etc., which is where I'd like to see improvements.
I will continue to use O2K with the Sun's ODF plugin v 3.2 for MS Office until LibreOffice comes of age (which I also have on my machine but only occasionally use as the 12-year old O2K is still significantly better than L.O. in many regards).
When Microsoft finally gives me what I really need instead of what it thinks I might need, then I might consider upgrading.
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An afterthought:
Seems to me that M$ would do much better if it provided a truly useful and functional feature such as a proper virtual 3D filing system that's fully integrated within MSO itself.
M$ failed to deliver the database filing system, WinFS, with both Vista and Windows 7 (and there's still no hint of it in Win 8 either). Integrating it, or part of it, into Office on a limited scale would make sense as it'd mean that years worth of files could be properly named, dated, indexed and cross-referenced by subject etc.
Moreover, a cleverly designed system would also mean that this additional metadata, which would be normally be lost when exported to a flat folder/directory-based file system such as XP/Win7 or Linux, could be integrated into both the file as additional metadata as well as into a section of the file name by some smart shorthand naming protocol.
For me, this would be the killer new feature.