For the first month or so the mileage was about 19 MPG for my 2006Sonata LX (V-6). Now that the break in period has been reached and it has about 3K miles, the mileage has improved to 24 MPG in mixed driving. That is right in the middle of the claimed EPA ratings. I have yet to take a long trip to see what kind of mileage it gives on the highway.
I own a '06 Sonata LX silver and bought it in 2005. Overall it's a great car, has everything I wanted other than a navigation system. I would, however, like to point out a couple of things that I've noticed. One is the suspension is harder on the LX's as compared to GLS (my cousin owns one) which I think is due to the 17" wheels. The other thing I've experienced is the body paint. Somehow the paint job on the car is not the best. I already have a small (approximately 0.5cm in diameter) chipped paint on the EDGE hood of the carand I can see the rust on it. Took it to the dealership, the estimator said that it is due to a rock which is kind of a strange answer because the rest of the hood didn't have anything. This paint is actually starting to get chipped off from under the hood since its on the edge.
Over all the paint is lousy I see small dots of rust on the trunk now where is no signs of "rocks" hitting the car.
I am very disappointed in the paint job done on the car. One and the only thing that would stop me from buying a Hyundai again.
I own a 2004 Sonata LX (v6) and the car achieved 29 mpg on the way from Florida to Michigan. I consistently drive 80-85 when on long trips. I was very impressed with the mileage (1 mpg) better than listed and I was flying.
I would like to comment on the bad paint job as mentioned above. Unless you were bombarded by falling rocks there would only be one or a couple of chips (not all over). Paint cannot protect your car from a rock at 70mph especially on the edge. The edge of any body part is doubled (folded) up because is a weak point. This paint chip would have probably occurred on any body edge of any car.
I may not have an 06' Sonata, but I do have the same problem with lots of orange dots on the trunk and hood on a pretty new car. My mechanic told me that it isn't rust, but that it's fertilizer or something like it that is oxidizing the paint. It isn't the paint's fault, or the finish, but something that's coming in contact from outside. I have a Honda, which is known for quality products.
I have done some long trips with my V6 Sonata, which believe it or not pushed my avg mpg ratings around 35-36 mpg! In mixed driving, I get roughly 28-30 mpg. I simply adore the car and look forward to keeping it for a few years after it is paid off! Great to see so many other people who have found the true value Hyundai gives its buyers!