Now I will typically go 45 in a 45 or even 50, but i sure am not going to get worked up over someone who doesn't go the full posted speed limit.
I will also tend to drive under the posted speed on highways. primarily for fuel efficiency. Around 65 is a sweet spot for me and i burn significantly less fuel at that speed vs going a full 70. Granted if I am on a long trip, an extra 5 or 10 knots makes a significant difference. 65 vs 75 over 200 miles is close to 30 minutes.
EDIT: Of course a 4 minute difference in commute, both ways, 250 work days a year. 33.3 hours. That's a day and 9 hours. Christ, that's 55.5 days at retirement.
Fuck it...people need to drive faster.