That's great mileage for sure! I have about 3,600 miles on my 08' sedan. I drive 17 miles each way to work and the first 5 miles is freeway, the rest, surface streets, but on some of them at 5:30am it can be like the freeway! I'm seeing between 32 and 35 mpg. That sure beats the heck out of my Tundra's 13!
I've gone to a little bit wider tire than stock with 205/40/17's. I'm thinking this may reduce my mileage slightly. Mostly my mpg is tied directly to my right foot.
I'm thinking about going to synthetic here real soon. I'm running Mobile 1 in my Tundra and after 128,000 miles the dipstick always shows right at the 'full' mark even at the 7,500 mile intervals that I change by.