I have been using Gnumeric for several months. Although people still use Excel, I have set Gnumeric as the main tool to open Excel file lately.
Excel for some unknown reasons cannot work together with the web conference system I am using. A ridiculous workaround is that while I am using the web conference system, I have to open Microsoft Net meeting. I guess some secret code from Microsoft only compatible with Net Meeting.
This is so annoying. I do not really need any new advanced features from Excel 2007. For me, Excel 2007 is a defect product if I can use an older version of Excel with web conference system without any problem.
I found that Gnumeric is actually faster than Excel in turn of opening the file and show data.
Almost all functions are compatible.