I stumbled upon the Scion Xd while looking for a Honda Civic and Mazda 3. The Scion is most different from the Mazda, but is similar to the Civic in the following ways: reliability, fuel efficiency, and compact size. The car is decently built for a compact car. It shares many components from the Toyota Corolla (engine, tranny, etc) and knobs and other items from the Rav4. For any 4-cylinder car that doesn't have a turbo, I recommend the manual for better control and performance, especially when merging onto the freeway. Overall, I'm very satisfied with my Scion and glad that I found it.
Fuel economy (I average 30 in the city and 38 on the highway), I find the driver's seat pretty comfortable and I'm 6'3". This isn't the type of car I would call amazing, but for my daily commuter it's more than I could ask for.
The biggest downside of the Scion Xd is the road noise - the engine sound and road noise is louder than I prefer. I plan on keeping the car for a while, so I'm going to install some Dynamat which should reduce the noise substantially. I wouldn't have purchased a Civic or Mazda because of the noise though.