...I have over 48,000 miles on my 2011 Fiesta and have averaged 36.5 mpg with roughly a 60/40 city/highway split. I've only gone under 30 mpg on a tank once or twice (in the winter due in part to slower city traffic speeds and excessive idling to keep the interior warm).
UPDATE: At 66,630 miles, and after having had to drive the 2011 SES during the winter months for the first time, my average is at 35.6 mpg with a 56/44 city/highway split. For comparison purposes, I've driven my ST 11,200 miles in the past six months averaging 30.4 mpg in 66/34 city/highway driving.