Has anyone used an app like Waze GPS?

Waze Social GPS, Maps & Traffic
Waze is the world's largest community-based traffic and navigation app. Join drivers in your area who ...
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The guy at work said that it warned him of speed traps, traffic accidents, provided proactive rerouting of your trip. Am curious if anyone has used something like this because I have been stuck on the interstate for hours waiting for emergency responders to address a major accident. (Am at work on duty today...)