The last time gas prices were heading towards $4/gal, I was driving a Subaru WRX STi ~150 miles/day to/from work. 22mpg was the best I could wrangle out of it. I calculated that, at 35mpg on gas costing $3.75/gal, the Fit would more than cover its own car payment in fuel savings alone. So I bought one.
I get closer to 40mpg these days, with some mods and some practice, and the car is paid off.
(I still keep the STi around, for those times when I fell rambunctious. Since I don't drive it much, I don't cringe when it comes time to fill the tank with 93 octane.)
Congratulations on choosing the Fit. The car is nimble, fun to drive, economical, and insanely practical as a way to haul stuff. I see yours is an automatic. MPG may be slightly lower around town when compared to a 5-speed, but it should still do quite well in steady state 45-55mph traffic due to its taller final drive.