I have a Fit as well. I do love it. It is a great around town car! It's not a fantastic "take a trip across the country" car, but it doesn't sound like that is why you would be getting one. I have a 2008 Sport with a manual transmission and regularly get about 35 mpg. The tank of the car is 10 gallons, so yeah, it is cheaper to fill up. I drove a Focus before this car that had a 14 gallon tank and I got the same amount of miles out of a tank, I did see a decrease in fill-up costs. I drive a combo of in town and highway driving.
I love the space in the car when the seats are down and the different ways you can configure the seats. I also got the rubber mats, which has been VERY nice, especially in such a snowy winter this last year. The car does great in the snow. My friend has a 2007 Sport with an automatic and gets lower fuel economy than I do...maybe like 27-29...but that still better than most cars. I also did get the trunk shade thing because I realized that there was no covered place in the car to leave anything.
Also, just a side note, 9 months after I got the car all the tires were stolen off the car in the parking lot of my apartment complex. So, I would HIGHLY suggest that if you get one you also spring for the wheel locks. If you look on Fit forums, getting the tires stolen off these cars is fairly common.