Delta and Northwest are offering bonus miles and elite qualifying miles for Hilton stays of two nights or more between July 15 and October 15. Registration is required. Delta or Northwest has to be your double dip selection as well, of course.
If you choose to earn variable miles, the offer is a bonus mile and qualifying mile for every dollar spent up to a maximum of 5000 miles.
If you choose to earn fixed miles, the offer is a bonus of 500 miles as well as a fixed 500 qualifying miles.