Airlines are now implementing new systems for paperless boarding.  Delta has launched electronic boarding passes in four major airports across the US; Memphis, Minneapolis-St. Paul, Las Vegas, and LaGuardia in New York.  With this new system, you can download your boarding pass to your cell phone or other mobile device up to 24 hours before your flight, eliminating the need for a paper pass.  Other U.S. Airlines that are testing mobile check-ins are American, Continental, and Northwest.   

Lufthansa has also launched a similar system where travelers are sent a barcode to their smartphones to clear security and board the aircraft.  They are the first airline to offer the service to their international customers, this technology had only been used for domestic flights.  Lufthansa plans to offer the use of the service for more flights in the upcoming months.  Since implementing it last summer, their number of passengers using the service has grown to 75,000 a month.