UPDATE: Enable your iPhone via Settings > Email > Mobile > Find my iPhone. Then go to me.com, login to your Account tab, and choose Find My iPhone from the sidebar. Voila! Thanks to everyone who sent this in. Screen grab after the break!
ORIApple just announced via their MobileMe News "blog" that:
Find My iPhone can be found at me.com today, but you also need iPhone OS 3.0 (available on June 17) installed on your iPhone to use the feature.
You can learn more about Find My iPhone by visiting What's New for MobileMe.
We don't see it yet, but if you're a developer already rocking 3.0 and MobileMe, hit http://www.me.com and let us know if/how it works for you!