Along with rolling out some nice GUI improvements to MobileMe (yes, I use it. It's simple, it works, and I don't have to mess with it.) last night for Mail, Contacts, Calendars, etc. Apple also released a "Find my iPhone app" available from the App Store.
In the past, if you lost your iPhone, you couldn't log into MobileMe from your buddy's phone (or iPad) and find your phone. Now, with this app, you can do that.
Grab the app: here.
Apple - MobileMe - News - Find My iPhone App Now Available.