It's funny you mention that, as our main business is the real estate search engine Nestoria http://www.nestoria.com We parse about listings 15M addresses in 9 different countries every day (though not the US). We work in pretty chaotic markets like India and Brazil. The world is a very diverse place, but there is one constant - agents do not feel the need to let themselves be bound by the "on the ground" truth of where a listing is.

Regarding Google, you are right, they do a good job, especially in the US. Full credit to them. The problem is the cost and usage restrictions.

Coming back to your initial point of reporting inaccuracies. What would be your preferred way to report problems? some sort of API you could automate? Would you just tell us there is a problem, or want to also tell us the solution?