I pay our quarterly estimated taxes with our AMEX. One of the big reasons we're paying out the a$$ for the Reserve card (more MQMs). Last year AMEX was running double miles on your April 15th tax payment....that was really nice (although they capped it at 20,000 miles). The convenience fees suck, but I think the MQMs and bonus miles at $30K and $60K more than make up for them.