Justin’s comments are right on. Anyone looking for a commerce solution that just works out of the box, is easily extensible, and is compatible with the themes available in the the WordPress repository needs to think about WP-eCommerce as a solution.
The peer-to-peer support for the WP-eCommerce platform is great, and the option for virtually round-the-clock professional paid support, from Instinct and others, if someone has a special need or critical issue should help people considering the platform for the small or large business make sleep better at night.
Anyone is who reviews the peer-to-peer support forums will observe that a relevant, articulate, polite, question or issue will almost certainly get multiple responses from the community, and very likely a response from one of the folks who work for Instinct.
-jeff