Trying to alter SKU field on ubercart product that is also a course I'm trying to modify a course (from the course module) and a product (from ubercart). I want to remove the SKU (right now I'm just testing how to remove the required bit) and a few other fields as I'm selling only online products. I'm not great at using hook_form_alter() yet.

I'm trying to follow this tutorial, http://www.ubercart.org/comment/8749/Re-Removing-SKU-product-edit-page and I'm not quite sure where he is getting $form_id == 'product_node_form' - is that related to the content type?

I'm trying to do this on a course content type, so if so, that would explain why it isn't working for me.
The ID for a node form is built up in node_forms():

$forms[$type . '_node_form']['callback'] = 'node_form';


Where $type is the name of each type retrieved from node_type_get_types().

So generally speaking, if the content type is product, the form ID will be product_node_form, if the type is course the form ID will be course_node_form, and so on.