*Sorry if you saw me post this in another thread earlier, I'm making this one because I can't edit the title on the other post, rendering it useless :/
Weekend 2 peeps with iPhones, have an awesome time, and please take a few minutes to get that app set up if you haven't already (a back-up wouldn't hurt, either.) It may be what saves you!
I lost my iPhone Sunday night (I had a screenshot of a friend's contact info as the phone's wallpaper) and when I got to the hotel I tracked it -- as of Monday morning it was still laying on the ground at Coachella, but I couldn't get back there to try and recover it myself before my ride left. I sent a message to Coachella's Lost & Found team and continued to track it. I filed a police report, and with their help plus the app's tracking beacon and remote alarm, I was able to get it back!
(By the way, Coachella Lost & Found contacted me a little while ago to say they didn't find my phone -- if you lost something last weekend and have yet to hear back, good luck and be patient, I'm sure they'll get to you soon!)
[Edited because in hindsight, too much detail can be advantageous to those of questionable integrity...]