Google Maps for Mobile has a new feature, My Location, in beta. I can't get this for the iPhone yet, but have read that it's coming. It uses the GPS on your phone to find your location, or, for those of us with phones that don't have GPS it shows your general vicinity based on the cell tower(s) you are connecting to.
I can definitely think of times I could have used this. Looking for a restaurant nearby, like in the video below, is one obvious example. Figuring out how to drive from where you are to where you want to be is another, but an approximate location for a starting point might work better in some situations than others.
Maybe those of you with smart phones that let you install applications will give this a try and let those of us who have to wait for Apple's blessing know how it goes.