United Visa has a promotion for double miles for paying your taxes, I believe thru 1/15/05 (don't have the details with me now-it appears this offer is not a targeted one and doesn't require any registration.) This promotion covers any taxes paid thru Official Payments-including property taxes and state taxes. I agree with other posters in that single miles at the cost of a convenience fee of 2.5% is too high. However, for me, double miles makes it worth it. We go on vacation to the Caribbean twice a year and coach alone is $800+ from California. So getting 80,000 miles by charging $40,000 in taxes and incurring a fee of $1,000 is still a good deal for us. I would not do it if I used miles for domestic trips as it seems you can almost always get cheap domestic fares if you are patient. Delta American Express will also probably have a double miles promotion-they usually do around 12/31 and 4/15 but I haven't seen it yet. Two things to be careful with on these promotions-at times they have limits on how many bonus miles you can earn (the United offer does not have any limits) and the cards themselves have limits on how many miles you can earn in a year if you don't have status with that airline.