I discovered today that the Hilton HHonors system cross checks information from the credit card number and airline/car partner numbers with your HHonors number. If you make a reservation and give a frequent flier number that is linked (in the database) to a different HHonors number or a credit card number that is linked in the database to another HHonors number, the system may not auto-credit you for points or miles.

This may affect those of you whose spouses/significant others share credit cards or may have family accounts (as with BA's Executive Club).