I usually try to shift at 2,000 rpm. On occasion, like when I need to leave a light in a little more of a hurry, I shift around 2200 from 2-3, and 2300 from 3-4.
I usually run 5th gear from 45mph up.
Driving like this, I always get 20+ mpg in the city. My mileage is actually usually worse on the HWY.....
--Jeff