The developers of OpenOffice.org have implemented some major improvement of memory usage for OpenOffice.org Calc. In their sample spreadsheet it reduces the overall memory requirement by 28%. I have some users of OOo complain to me that Calc could not handle very large spreadsheet and it so it was very slow. This could be a major step to alleviate their pain.
Don’t hold your breath yet, because this improvement will only come to you with release 2.3 planned in September 2007.