One the one hand — cool and very useful way to avoid traffic jams. Good excuse to buy an iPhone so you have a screen large enough to make sense of whatever data map becomes available.
On the other — why are so many people driving and talking on the phone at the same time? Eek. And the ability for someone to sign up to track their kids (or, more accurately, their kids’ cellphones) and/or spouse (‘s cellphone) is a bit much.