The major difference is that the syntax of the commands is different
and also if using advanced features such as macros then these are very
difficult to import between Open Office and MS Office - then again,
macros can have problems between MS Office versions !!

So a lot depends on how complex a spreadsheet is needed as to how well
it will port between MS Office and Open Office. One thing to note,
save the spreadsheet in MS Office format as the Open Office one will
not even be read otherwise !