On a further note, I would also recommend testing WP Ecommerce *and* your categories/products importer plugins against PHP 5.3 and MySQL with strict mode turned on.
I failed to even get the importer to work on my development environment, and by enabling WordPress database errors to show I uncovered the reason:
WordPress database error: [Field ‘description’ doesn’t have a default value]
wp_wpsc_product_categories (… )
My MySQL database runs in strict mode, and you can’t be lazy!!! (Seems like a WP e-Commerce issue this one, though)
Just a side note…