Most people are missing some of the most amazing stuff here. First, how the slider works without refreshing the tiles. They have tiled the travel costs http://tiles.trulia.com/commute/time_map/data/driving/37.774... and are drawing these changes without having to refresh the map. That's cool. Secondly, they have used Openstreetmap for calculating travel time. I cannot imagine OSM having a street segment cost that is too accurate, so it was probably derived from pure geometry (think about it... traversing .25miles in downtown SF has a much higher cost than .25 miles on the 5 freeway). If instead, you used a Navteq or Teleatlas dataset for this, I bet the isochrone polygons would come out much more accurate. My hats off to the Trulia team, this is good stuff.
The physicist in me won't think it's cool until there's some monte carlo simulations of commute times with some additional random walk information for alternate routes and stop light entropy, then a log-likelihood fit to find the best fit commute time.
Just kidding, it's alright, it's kind of off for the SF/PA commute though, by nearly a factor of two for many places in SF, unless you're doing absolute worst case scenario every day of the week.
