Delta SkyMiles members can earn a 50 percent mileage bonus on hotel, car, limo and shuttle partners through April 30, 2010. To earn the bonus, register and complete three or more qualifying partner transactions. For example, you can stay at a Marriott hotel, rent a car with National and take a ride with SuperShuttle. Or you can stay three separate times at Hilton since multiple transactions with the same partner will count as eligible activity. After you meet the minimum requirement of completing three partner transactions, you will earn a 50 percent bonus on all of your hotel, car and ground transportation activity during the promotion. Transferring hotel points into miles also qualifies as a transaction. Registration is required and you must register at http://www.delta.com/staydriveride before completing any qualifying activity to be eligible to earn the bonus.
Bottom line: There is no limit to the number of bonus miles you can earn with this promotion so creative use of partners can help you rack up some miles.