Another way is to give the platforms the SINE behaviour. Takes a little bit of trial and error to set the magnitude but I can usually get it within a couple of minutes. Looks a little nicer imo due to the easing in and out.
Just another alternative :)
Platforms
This is also a good reason to point you to my request for a path plugin. That would be perfect for setting up moving platforms. Put your marker down here ;)
PATH request.