I use MobileMe, because I want an online cloud storage for files and I anticipate that it will become free quite soon. It's not perfect, but I have faith that Apple are working on it. One of the unexpected benefits (indeed for some the sole benefit) is that you can use it to locate your iPhone, send messages to the screen, and indeed wipe all the data remotely. Provided you set it to allow push notification (which I don't), it's pretty cool to think that if some random knobhead steals your phone, you can send a few lines of abuse before crashing the entire device.
However I was surprised to see this as an iPhone app. If I've lost my phone, I can't very well use the app! According to Apple:
if you lose your iPhone or iPad while on the go, simply install this free app on any other iPhone, iPad, or iPod touch to find it