Using WP e-Commerce on a WordPress multisite is easy. But getting it to work with Domain Mapping proved a little tricky.
WP e-Commerce adds a few options to the wp_options table, like “product_list_url”, “shopping_cart_url”, and a few others. These are full links containing the domain name from your multisite setup. If you want your customers to be able to update your basket and checkout, you must manually change these urls in mysql, to contain the full urls to the domain you have mapped.