Here is an example of the cost savings:
Price of Lady Dior in Medium Lambskin is 2200 Euros (November 2011)
Exchange rate 1.28 US Dollars/Euro
Cost without accounting for your credit card's foreign exchange rate = $2,816
VAT reduction of around 10% when you take away the processing fee: ~ $2,534
Price of the Lady Dior is the US is $3,100 and if you add sales tax it would be $3,355.75
Total savings will be around $821.75.
The exchange rate is very low right now so if you plan to go to Europe soon it will be best to wait to purchase in Europe.