Office 2008 on all my PowerPC Macs and Office 2011 on the MP at work.
I was using Office 2004 for several years, both at home and at work. For a few years I was the only one at work that could open .docx, .xlsx and .pptx files. Now that most of the PCs have been updated that's not necessary.
We use Office 2008/2011 every day for production work. All of our legals come in Word format and we get a cable tv guide from the City of Glendale, AZ every week in Excel format.
Here is a major difference between Office for PC and Mac though. On the PC, if you track changes in the document and make deletions or additions it shows you those in little frames on the side of the document. On Mac, however, changes are tracked in red UNDERNEATH where they are edited. This makes it DAMN DIFFICULT IF NOT IMPOSSIBLE to simply cut and paste from a PC document with tracked changes that's opened on a Mac. Because all of the additions AND deletions are copied too, not just the final edited text, which is all that should be copied!!!
We have to specifically instruct people at the cities of Glendale and Peoria, AZ to NOT use track changes on their documents. There is a work around where the Legal Manager can copy and paste to a new document on her PC that does not have track changes, but this is a PITA.