I love my Mazda3, but the brakes are strange. The rears do wear out much faster than the front, but the fronts last forever. It's got huge front brakes -- quite a bit bigger than even my Mazda6s has. It looks strange to see a car with so much brake dust on the rear wheels and none on the front.
Fuel economy, as you mentioned, isn't great. I don't care what Consumer Reports says. On the freeway at cruise (about 80-85) it gets no better mileage than my 6s gets on the freeway at the same speed -- about 27mpg. With the wife dawdling along (very slow) on her very-high-traffic freeway commute it doesn't break 30mpg.
The seats are hard, but not uncomfortable by any means. I prefer my 6 for long-trips, but I've done a number of 1000-mile trips (single-sitting) in my Mazda3 with no problems at all.
The downside of the Mazda3 is that it can get quite pricey if you're looking at the higher end. And there's usually little room for negotiation on them either. My Mazda3s cost more than my Mazda6s.
