I've never been any closer than 15% battery left.
Well I was away from the house today and we needed to find a place to eat - so I used some GPS intensive programs and then let the GPS take us to the place.
When we got there it was at 0, the phone shut off. I lost my map settings (not hard to put back).
Today before using maps I was doing great around 80%... then in an hours time it was dead. So I can see why people say GPS drains the phone.
However I do take exception to people who turn it off all the time. It uses no battery at all unless you use an application that is using it all the time.
By the way maps is killer.