I just found this out, so it’s time to pass it on!
If you lose your iphone, ipad, or ipod frequently, you can use mobileME to locate/wipe/lock/send messages/tones(2 minute long! Helpful if you lose it around the house). You can also use the Find My iPhone application, to search any devices attached to your account that you set up. You can use Find my iPhone for free with iphone4, ipad, or 4th generation ipod touches that have iOS 4.2 installed. If not, you can use the paid subscription. Here is the link on how to set up the free account :
http://www.apple.com/iphone/find-my-iphone-setup/
Hopefully this helps someone out :).
update :
You can create a free Find My iPhone account on any iPhone 4, iPad, or iPod touch (4th generation) running iOS 4.2. Once you create an account on a qualifying device, use your Apple ID and password to enable Find My iPhone on your other devices running iOS 4.2. Find My iPhone is not available in all countries.
Great news if your spouse/children/siblings are using a 3GS/3G! There’s also a way around it if you only have a 3GS, have a friend with an iphone4 log in and set your free account up for you. If you need more details, ask, and I shall post.