The debate that Microsoft has on cost per seat is dwarfed by retraining costs - which may actually be lower for LibreOffice than the transition onto the ButtonBar in Office 2010. Of course, Windows is going to move to Windows 8, and Linux desktops will be more familiar than ever...
Personally, I've moved over to LibreOffice, writing a Python addin to get Bloomberg compatibility. My users are on LibreOffice for word-processing (practically no-one has noticed), for spreadsheets I'll let them flip back to Microsoft Excel if they have 'power user' problems/mindsets - but often find that they are taken aback by the button strip anyway.