Generating S5 based presentations from an Org Mode file is something I've considered for a while. I've just published some working code to do so: http://github.com/sigma/org-s5 The README file should give the basic steps to make it work.
Constraints I wanted to respect:
This is probably far from being complete, but at least it's usable enough for me to do presentations at work.
Hope it can be useful for someone else.