After over four years of ownership, this is a great car all around. I've driven this car through mountains, snow and floods and still after 44,000 mi, the engine and everything else still runs like it did when it rolled off the showroom floor. Acceleration is nothing special, but it's ample to get on the highway and keep up with traffic. I usually average about 34 mpg with mostly city driving, 42 mpg is the absolute most in my experience. Storage is never a problem even on long trips with a dog kennel in the back and being 6'2 I have plenty of headroom and legroom (maybe not so for rear passengers). If you're a no frills person looking for reliability and function, Yaris is a great choice.
Proven engine reliability. I also enjoy the handling around curves. Not a lot of body roll, stiff and holds the road very well, even in adverse conditions. It's one of the last few cars where you actually feel connected to the road with no ESC, sound dampening and other nonsense for lazy drivers.
Seats are a little hard for long rides (200 mi+), but this isn't a touring car. I wish the windshield was a little taller as I have to duck often at red lights.