I just bought a 2011 Sonata slightly used with 9k miles on it and got a great deal from a Dallas, TX dealership. I traded in my Chrysler 300c Hemi - I was sick of driving it from gas station to gas station. What a revalation the Sonata is! It is so much easier to drive and cornering is way better than the 300c which just felt like a tank. Yes the Hemi had more power, but the Sonata is lighter and really does need it. I was very curious about real-world gas mileage so the first day I bought it, I took it round trip from Dallas to Plano and back on mixed city/highway driving. I averaged 35.7 mpg on the freeway cruising at 75 mph - I am sure if I went slower, it would probably be closer to 40.
I have loved the shape of this car since it came out - it is so much sleeker than a Camry or Accord or even the new Altima - they all look so incongruent in design - this one just flows all the way around - and the new Passat, I am sorry but it is boring! I love interior, I got one with Nav and blu tooth and of course, the MP3 direct input. My Hemi did not have blu tooth or MP3 input or even an aux.
It is not quite as quiet as I remember the hemi was, I think the tire noise is a little more obvious but not too bad compared to a Honda Accord. Also, the engine is a little buzzy but generally smooth overall. I am looking forward to my (almost) new Sonata in Sparkling Ruby metallic. This is my third Sonata - I never had any trouble with the first two, I just trade cars a lot.