I had bought a 2008 Yaris sedan 5 speed manual and sold it to my son. There was a good deal on a 2010 so I bought another one.
I am an ultra light foot driver and can consistently get 42-46 mpg in the spring or fall when I can have the A/C off. During the summer I can get about 41-42 mpg and because of our below zero winters I get into the upper 30s for mpg. Overall year round my average mpg is 41.7. The key seems to be the aerodynamics of the 4 door sedan and the manual transmission. Not sure why this car is not rated at better mpg. Could be it is driver style sensitive in that a lead foot driver can get terrible gas mileage and a light foot driver can get easily into the 40s for mpg. I have driven this car 52000 miles to this date April 2013. I use this car to commute to work which includes rush hour traffic. I have also used this car to go cross country from the midwest to Florida. Total MPG so far 41.68.
Toyota has consistently made cars with about 20lbs per horsepower. The Yaris is no different and because it is light weight it is surprisingly peppy especially with the manual transmission. The only draw back is it can be jittery on the highway and side winds can be felt though never a problem. Winter time traction is at best fair but you just need to drive accordingly. I plan to get good all season tires to see if this helps.
I am a stickler on maintenance and was very disappointed on the driver side drive shaft seal leaking twice! I was not given any reason why this would happened but so far since the last repair it seems all is fine. I change my own oil and was able to notice the problem way before it was serious as I notice an oozing of manual transmission oil around this drive shaft. I have not been able to find this is a common problem though.