Originally Posted by drluccia

2007 Limited Roadster, NA, I get 26-28 with mixed local and highway driving, but generally under 70 mph. On the drive from Tempe, Arizona where we bought it to our home in southwest New Mexico, I got 30 and that was with hard-as-rocks ancient tires and average speed of 70-80. Almost always use 91-93 octane gas ... added a half tank of regular on a road trip because Premium was really overpriced. Car ran fine. Completed a preventative transmission service last month, feels smoother and a little quicker off the line, but a lot of that is me becoming comfortable with the capabilities of the car as my capabilities increase.
Yes, mileage is a good diagnostic, especially if there is a sudden drop in mpg. It's an early heads-up.
And I do not drive with an eye on the gas guage. Driving this car is too much fun to worry about mileage ...