Aside from the quality issues, and the notorious bugs in Office over the years, the UI is disgusting. The whole 'ribbon' thing should have been tossed years ago.
I had one client take a look at the 'ribbon', and use a trial version of Office for a month, and they totally backed out of getting it, and went with OpenOffice.
There are *some* businesses that value PRODUCTIVITY over DUCK-DUCK-WADDLE-WADDLE and find that they can function far better without blindly following everyone else (off the cliff).
Heck, Office isn't even compatible with the Open Doc 'standard', and even with documents from some previous versions of the suite!