Speed is essential for OpenOffice.org
When they say large spreadsheet, they mean really large, 25 megabytes, 100 sheets, 1 million cells and hundred thousand formulas. A change in the algorithm used brought down the times from ~39 minutes to 2:37 on a 1.8 MHz Pentium IV. On a Dual Core AMD Opteron(tm) Processor 275 with more memory, the time reduced from ~28 minutes to 43 seconds, almost a gain of factor 40.
Unfortunately, the improvements will only be included in Release 2.1, targeted for end of the year. Hope for a nice Christmas present.