I recieve a spreadsheet once a week that is created in M$ Excel. When I look at the file in a hex editor it appears to be created with the version of Excel in Office 97.
I have not been able to find a way to view these spreadsheets correctly. I've tried OpenOffice.org, gnumeric, and kspread. I haven't tried Crossover Office yet. I know that these spreadsheets have got graphs and action buttons. These do not work under any of the programs that I mentioned.
I think that if you trade documents with people in or out of your organization who use M$ Office you may have some compatibility problems. If, on the other hand, you don't exchange documents with anyone using M$ Office then you will probably be happy. I use OpenOffice.org suite for my own documents and I'm happy with the results. Keep in mind that I am not a document power user. I do a little bit of formatting but my documents are all very simple.
OpenOffice.org software defaults to using the open document formats. If other document software applications adopt these file formats then in theory documents will be easily read and edited correctly by all applications using these file formats. You can be assured, though, that M$ will not adopt open standards.