I found that running Openoffice on a fairly old laptop (500MHz, Neomagic 256XL+) became intolerably slow (it used to be fine with older versions, I think!). Rendering (redrawing) a page of text could take 3-4 seconds, and pages were frequently re-rendered unnecessarily.
Turns out that what is going on is that OpenOffice does its own font anti-aliasing, using the OpenGL X extension. On my laptop, this turns out to be incredibly slow. Other applications (Firefox, etc) do anti-aliasing no problem, but Openoffice does it differently, and at least an order of magnitude slower, it seems!
Solution: in OpenOffice's Options, go to the View section, and de-select anti-aliasing. Not as pretty, but a lot less frustrating!