I was excited when this was announced, but I'm not sure what it's actually doing in practice. On my Android 2.3 phone with up-to-date Maps app, it always picks the first of three alternate routes, even if the others have shorter estimated times and no lengths of red.
I've compared Google Navigation on my Android to Maps on my wife's iPhone, and sometimes they pick different routes. After checking the traffic, our conclusion was that mine was choosing the route with less traffic, while hers was always choosing the most direct route. I think it just re-orders them so that the chosen route is always first.
