I have played the credit card game for years to wrack up mileage. AMEX is the only one that will actually track you and refuse you if you try to get a card within a year on canceling. Right now I have six cards of which four are with airlines. Latest is with CitiCards on AA. 25,000 and no fee for a year. It'll be canceled when the year is up. I have done that over 10 times with CitiCards. We charge virtually everything so the miles really accumulate. The key is not to accept their offer when you cancel that usually means another year fee free and maybe 5,000 miles.

With Delta we booked two first class tickets from Boston to Sacremanto for the first week of June. Both for 45,000 miles. Sometimes it actually is easier getting flights and using less miles when booking FC. Delta has a bizarre scale that they use regarding miles and it can be costly especially for prime destinations. The key, as always, is book well ahead of time