Open Office is good software. At least the 2.0 previews I've been using.
I used to openly mock StarOffice: ugly, clunky, Java where you don't need it, incompatible, slow. Then again I used to make fun of Firefox, too, and look how wrong I was about that. I've been using OpenOffice 2 exclusively on my new computer, particularly the spreadsheet. And it's quite good! Basically, well, it works exactly like Excel. No better, but just as well and it's free. If anything, it seems even faster than MS Office.
I've only run into one problem importing from Excel. Some of my own spreadsheets have some funky formula that work in MS Office and not OpenOffice. On import they get replaced with #NAME with no hint what the broken formula was, so I can't fix it. But that seems unique to my crappy spreadsheets, documents from others have worked fine.
It'd be nice if I could say OpenOffice were better than Excel, but it's not. At least for the simplistic things I do. Well, there's one improvement: the UI doesn't jump around confusingly when I type a space in a formula, trying to let me pick cells by the keyboard. It just lets me type. Nice.