It looks like on a paginated pages in the store, the previous And next links are going the wrong way.
And I think there are in the wrong place:
1. on the first page it sows previous: http://wp-ecommerce.org/store/
2. on the last page it sows next: http://wp-ecommerce.org/store/page/4/
3. should those links really be there? http://wp-ecommerce.org/store/page/3/