Comment Nor is Star Office (Score 1) 375
Our local government organisation moved over to Star Office (a close relative to OOffice in 2005. I was told in 2009 that they had more MS Office installations than in 2004. The reason - imperfect conversion to MSOffice formats when they want to exchange documents with outside organisations. The differences are generally small. They (the Council) are now giving up and moving to MS Office 2010 (at a time of tight budgets) though I hope and expect Microsoft are giving them a great price.
Like the parent to this comment I like the idea of OpenOffice but that never compensated for my liking VBA more. Purists will mock - why else come here - but I think VBA is a terrific extension of Excel.