@mikerspencer@vicgrinberg@knud Since a Mac + Keynote uses HDMI as its output, there's no excuse for organisers insisting on a PC / PowerPoint / in advance if it doesn't suit you. You should only have to worry that it works on the laptop you create it on – everything else is their responsibility.
Often I find that the technical people at the sharp end are absolutely fine with this & will make sure it works. It's often the admin organisers in between who are clueless.