I am disapointed by the shipping options available in the cart creator. Paypal cart has a very useful way to calculate the shipping, based on a variety of order values.
Although there are numerous options available in the cart creator, quite complex ones too, like % of the order value and so on, these are all the wrong way round! Shipping costs should get cheaper when you buy more goods, not more expensive - until you get to an order value where shipping is free.
Its not a good idea to let the customer pick the shipping cost. I had encountered this problem in the google checkout. If you ask the customer to pick the shipping charge relevant to the order value, they pick the cheaperst irrelevant of the order value.
I thought of a way of calculating the shipping cost which would suit me:
a) say the default shipping is £6 = min schipping charge
let the customer select better deal in the additional shipping options
b1) shipping cost per item, say £1.50: if he only buys up to 3 items, he will save with this option
b2) shipping cost is calculated as 10 - 20%of order value (positive only): if he spends over £20 he will save, until he arrives at free shipping for orders over £50

Most online retailers let you select the shipping options, such as amazon.com for example. I know there are not a whole lot of shipping options on this version of the cart creator, but the pro version will address some of the shipping issues. Which ones, no one knows yet.

The best shipping method hands down is the way Zen Cart incorporates the USPS shipping module available by the USPS. Shipping is calculated by total weight of products and destination zip code. The buyer selects the method - i.e. ground, 2nd day air, etc...

I'm hoping that the Pro version will do exactly this. Simple and acurate shipping method.

I know this doesn't help non-US stores but it is great for US based stores.