On the freeway here, they upped the limit to 90 from 80 because so many people were going 90 anyways. The result was that everyone goes 90, and people in a hurry usually stay around 100. Nobody is getting tickets on the freeway anymore, but police are heavily enforcing both school zones and main arteries in the city.
I've passed patrol cars doing well over the limit and had them follow me a distance. As soon as it's clear to them you're just a guy in a hurry, they back off and go about thier own business. I have never gotten a ticket in this city, and I know I've been speeding.
It's nice to have the police going after the real problems on the roads, not people trying to get to where they are going, but the people that really have no idea what they are doing behind the wheel of a 3000lb pile of metal.
If traffic is going 90 in a 70 zone, just go 90. You'll see a decrease in people tailgating, and a huge decrease in cars swapping lanes to get ahead. I really don't care if your mileage drops 2%.