It is pretty acruate for Boston area. It seems to update about every 10 minutes but I have found that traffic conditions tend to change even faster than that. It is good enoughfor em to figure out when to leave work for the ride home though.Don't put your faith in the traffic feature. I live in NY and drive to NYC 4 times a week. Everytime I get stuck in a traffic jam on the highway I check my phone to see if the traffic is on Google Maps and I have yet to see it show up in red or yellow. I don't know how often the traffic info is updated but it can't be that often.
I have my commute routes set up in traffic.com, and I think it's WAY easier to load those pages now with my iPhone than it was with any of my previous smartphones (except for the BlackJack, which had 3G). Also, using WiFi on the iPhone, the page loads just as fast as it does on my desktop. You still find that's too slow? I usually check as I'm walking out the door from home or work. By the time I'm pulling out of the garage, the page has long been fully loaded. Since I have two different routes I can take - both on highways - traffic.com is a lifesaver for me. My commutes are very traffic and highway-accident dependent.Correct it only works for certian cities. Cities that have installed the necessary infrastructure for real time monitoring of traffic. There are numerous companies that are providing the traffic info like SmartRoutes and NavTeq. It is just not available in all cities yet.
I used to use websites like traffic.com to check traffic before I left work but those are way to slow, even loading up googlemaps on the computers is slower than turning on the iPhone. So I just use iPhone now.