Anyone who has an iPhone with version 3.0 (released today, June 17 – hop onto iTunes, sync/backup the phone and search for new software) and MobileMe NEEDS to enable FindMyiPhone. TUAW has a great little tutorial about setting it up with the new iPhone software and MobileMe.
I tried it this morning and what the system does is find the location of the iPhone so you can go and find it. After about 3 minutes the system will locate the iPhone on a Google Map so you can know if you left it at home, in the car or at the office (or in the cab you just got out of).
The next neat part is if the device is in a cab for instance, you can send a message to the device requesting that someone kindly return the item to you. If you want to be even more annoying you can sound a tone for 2 minutes as well (which is also helpful if the phone is stuck between a few couch cushions).
Lastly, you can wipe the device – if there is no note or knock on the door from a nice cabby, from the MobileMe page you can wipe the device clearing off all your contacts, movies, photos, music and email so the person that now has the shiny iPhone can only start from scratch (but at least they are not starting with your address book).
Good job Apple!