Keynote PDF Export - black text appears white on some computers, but not all - why?

This problem seems to have been going on forever, why is there STILL no solution? I'm really keen to mover over to Keynote, cos Powerpoint is very cumbersonme and frustrating in my experience, but I'll only ever use Keynote to export PDFs for presentations, so if it can't even get this basic function right, there's really no point in abandoning Powerpoint - at least I know my docs will come out fine and won't have to be embarrassed when clients come back to me frustrated cos they can't read the text!

Any thoughts?