Update: Apparently American Express and Uber have set boundaries for where this credit applies. Some people have been denied the credit despite taking rides to within the five burroughs. You may want to confirm with Uber that your destination qualifies before taking the ride.
Uber and American Express are teaming up to offer Platinum & Centurion cardholders who visit the LGA Centurion Lounge two free Uber rides to anywhere in the five burroughs of New York City from Laguardia Airport.
This offer expires at 11:59PM EST on December 31, 2015. Must apply the promotional code to your Uber account prior to taking your ride. Offer only applicable to fares from LaGuardia Airport to the five boroughs of New York City. Eligible fare includes taxes, fees, tolls, and surge pricing. Promotional code will be provided upon entry into the Centurion Lounge at LaGuardia Airport. Lounge entry requires presentation of a valid Centurion Card or Platinum Card, a government-issued ID, and a boarding pass for the arriving flight.
The codes work for both new and existing customers and are given to eligible cardholders upon visiting the lounge. If you are new to Uber, you can find a sign-up link and other cool things here.
HT: The Points Guy