[From Hans] Google Maps for mobile gets even better. "What if you could do a little something to improve the world during your daily drive to work? Here are a few ideas: tell everybody in the city when you're stuck in slow-moving traffic; warn the drivers on the freeway behind you that they should consider an alternate route; tell the people still at home that they should spend another ten minutes reading the morning news before they leave for work; tell your city government that they might want to change the timing of that traffic light at the highway on-ramp. Of course, you can't just get on the phone and call everybody, and your one traffic report from your one spot on the road might not help much anyway. But if everybody on the road, all at once, could tell the world how fast their car is moving, and we could make it easy for anybody to check that information on their computer or cell phone, well — then we'd be getting somewhere.
If you use Google Maps for mobile with GPS enabled on your phone, that's exactly what you can do. When you choose to enable Google Maps with My Location, your phone sends anonymous bits of data back to Google describing how fast you're moving. When we combine your speed with the speed of other phones on the road, across thousands of phones moving around a city at any given time, we can get a pretty good picture of live traffic conditions."
The GoogleBlog for the full read.