To be fair to the poor guys at WP E-commerce and the whole Get Shopped / Instinct family, I did manage to get many years of very good usage from their software once I figured it out. It simply was never without bugs, and certain parts are insanely not obvious to the layman.
Let us take a great example. Variable Products. Variable products are products which have options, like small, medium, and large, or red, blue or green. With WP E-commerce, the options you add to a variable product create product variations, each of which creates its own separate entry on the DB and the sitemap as a distinct URL. The problem becomes when you have a products that comes in 32 colors, with 6 sizes, and 4 materials, and 4 neck style, and shortsleeve or long sleeve. How many variation / entries in our DB did we just create when using WP E-commerce?