one thing that many of our testers reported, that the exported HTML5 Publication doesn't seem to work. Testers tried that by dragging index.html into a browser or opening it with a browser.
So please note:
You cannot drag the exported index.html into a browser or just open it via a browser on your machine. Please either use the preview button (at the lower left hand corner of your document window) or deploy the exported files to a webserver first, and then open index.html in a browser.
For your customers you should of course host the exported HTML5 Publications on a publicly accessible webserver.