Besides that, when displaying realtime shipping rates for "Individual Items" on the product detail page, you want to be real careful as the rates are not accurate & are often displayed much higher than the realistic shipping rate calculated within the Cart. For example, if your typical order is for single, high dollar ticket items such as 55" Plasma tv's, then you are most likely fine displaying the shipping rate on a per item basis. However, if your typical order consists of many individual items, or perhaps multiples of individual items, then the actual shipping rates a customer will pay will be calculated far more accurately at the cart level. So in this case you would be shooting yourself in the foot to display shipping rates on the product page on an individual single item basis.
In my experiance most customers are capable of working out that the more they buy the cheaper shipping often is.
I think each product type is different, if you sell large items often you have fixed costs and it is just 1+1+1 = 3.
Small items cost a lot in the uk to post it's killing things like magazines when a £5 magazine cost £3 to post. And its not till you get over about 2kg that you can save money by using service that resell postage. It's bloody daft that I can got to the postage office and pay £70 for a parcal to be sent or I can sit at home and pay £12 for the same parcal to be picked up by the same service and sent to same place.