I wrote them and got the following back:

Thank you for your comments regarding your dissatisfaction with the increase in the conversion fees.

Diners Club periodically reviews its fee structure to ensure that the fees we charge adequately cover the real costs associated with the transactions. By assessing these fees only "when" the transaction occurs, we are able to offer credit, value, and superior services to you our Cardmember.

When a charge is incurred in a foreign currency, we will convert the charge into U. S.dollars at The Wall Street Journal conversion rate in effect the day we post the charge. Our 2% fee is consistent with our major competitor American Express.

I am sorry I cannot give you a more favorable response. We truly value you as a customer.