My advice, if you lost your Iphone, don't bother looking for it. MobileMe could be useful to remote wipe.
Do you think, you can find your phone if it is on someone's house. Let say you find your phone's location. There are few houses around it. Are you going to knock on each house and tell them you think they got your phone? What if they told you they don't have it. Will you then call a police and have them search the house? I don't think soo.