The latest version has a whole new set of problems compared with the last. Our products are all unique. When one person would add an item to a cart and then abandon it, the item would be removed from inventory (so no one else could purchase it).
The Paypal gateway would freeze. I have tried to install and use this solution for several clients and each time have ended up moving to another solution.
I have built carts with a lot of different solutions. I am still looking for the wordpress easy cart solution for the novice client.
I have tried Tribulant Software's WordPress Shopping cart and although it looks good, is just not up to speed under the hood...don't waste your time with them.
I have successful carts running on wordpress +biznify theme +cart66 and i have also had success with Magento Community Edition, but you really have to be up on your programming or have a budget for design, optimization, implementation with that product.