Why does my shop keep displaying the home page no matter what products I click on?

This problem may be that your shop is turned off in the settings.  Go into the sunshop admin, and look under Settings -> Shop Settings tab.  Make sure the store is turned on. 

I noted in researching the issue that the $_GET variables seem to be washed out, though $_REQUEST does still work.  I guess the code deletes all the GET globals when the shop is turned off, so all requests will redirect to the homepage.