I have two years of driving Coachella as a cab driver. You cannot flag cabs off the street anywhere near the Festival. There is one pick up and drop off location for cabs at Coachella. When the concert lets out, it can take up to an hour and half, waiting in the most horrible line that barely moves to get your cab. Yes, you can take a shuttle to your car, but then you have to drive your car possibly buzzed to your hotel.
People are booking their own personal driver to use in their own personal vehicle, that will act as a "Johnny on the Spot" driver, getting you anywhere you need to go safely and no risk of DUI. People without cars, are booking their own personal driver with vehicle. You can easily do this by looking in the transportation section of the Palm Springs Craigslist. Its generally cheaper to have your own driver, than use cabs (when you factor in total cost shared by you and the rest of your friends), and much more efficient than waiting for some yahoo cab driver to come pick you up, or waiting in some fucked up line to get a cab.
This year, I am not a cab driver any longer (thank Christ). However, its just so happens that I have a condo in Indian Wells, which I am renting out for weeks one and two, and will include me as your personal, on demand driver, either in your vehicle or mine.
Check the add here http://palmsprings.craigslist.org/vac/3726206628.html.