Hello Eric,

This is amazing, actual emacs lisp code from my explanations, thanks  
a lot!

If welcomed, I have a few comments related to how I currently use  
this function (I have a talk coming soon :-) )

     - If all "star" headlines become slides, it quickly leads to  
awkward layouts with empty slides below one star headings.
       I made a modification to the code to choose only one star  
headings as slides. This way, level 2 headings can be used as "in  
slide" headings.
       I used an (if (looking-at "^\\* ") XXX) in the preprocess hook  
for that.
     - An actual "title page" seems more appropriate, so I added one  
with "title author date" as h1,h2 and h3 headings.

The css need to be tweaked a little bit to get nice results.
My modified org-export-as-s5 function is attached.