A couple of links relating to the ubiquitous Microsoft Office.
Firstly, a look at how the new versions of Office for Mac and Windows compare over at How Does MS Office for Mac Compare to Office for Windows?
And secondly, a link through to an article that notes that the recent Service Pack 3 for MS Office (for Windows) will disable Office’s ability to open a number of different legacy file formats. Not good if you have a set of older documents that you open occasionally or are maintaining for archive purposes. You can ‘undo’ the effects of this ‘upgrade’ but it involves Windows Registry hacking (yuck). Or you could install OpenOffice to access some of the older formats. See Microsoft Office Drops Support For Older File Formats | Compiler from Wired.com.
I can see an increasing need to have several different virtual machines on one’s computer that allow the booting into legacy operating systems and running of older versions of software – sort of like RLP here post-switch to Mac OS X.