Actually I use OO's calc tool to manipulate enormous machine generated .csv files that cause Excel (any variant) to segfault and go down in flames. Hundreds of meg in a go? No problem, even on modest hardware.
For me, where OO really shines is the equation editor. Unlike MS Word you can compose complex equations without having to constantly bat your hand between keyboard and mouse. It's a beautiful design. Not as powerful as LaTeK, mind, but good enough for government work.
Where OO suffers is when you convert to and from the Microsoft file formats to the open formats; I waste far too much time re-doing PowerPoint graphics foo, redoing margins in Word, and so forth. Suspect it's a combination of differing font configurations between a Linux and Windows box, combined with non-standard or undocumented cruft in the MS file formats.