Re: Just get the best tool for the job...
If you need to retrain all your staff to work with Open / Libre -Office while they're already fully familiar with MS Office then going open source might not be the best of ideas for that specific part.
How did they become familiar with MS Office -- was there training for that? If not (and there hardly ever is, which is why most users use office software so ineptly) why would you think you might need to offer retraining for different software?
If you think MS Office 2003 users would have needed retraining to use LibreOffice I hope you also accept that they should have been retrained to use MS Office 2007 with it's radically different UI.