This video out of the UK makes the case that cities and towns should implement a blanket 20 mile-per-hour speed limit:

Over at Livin' in the Bike Lane, where this video comes from, they note that slowing down traffic "reduces the number of accidents, injuries and deaths... [and] revitalizes the neighborhood by encouraging more people to walk and bike." I'm all for bicycles and great streetscapes, but traveling 20 miles per hour in a car feels slower than doing the backstroke through cold honey.