I live outside Tampa, FL in a mostly suburban environment. For the last four months I have consistently averaged 30MPG. This month I am averaging a little over 28MPG. The difference is that the last 4 months had little A/C use and the last month has had constant A/C use (I see 2MPG hit). My driving patterns are:

1. average trip about 15 -20 miles, travel about 12k miles/year
2. interstate driving is about 20% of the total
3. I am a conservative driver (easy start/stop, stay speed limit) - no hypermiling techniques.
4. typically two people in the car all the time (myself and wife)
5. do keep tires at 39 PSI

Hope I captured the essence of what you wanted to know.

2006 HiHy base version