VERY IMPORTANT:

If anyone is considering DL, be sure to check out the changes that were announced today. It's posted on delta.dumb (the DL website) and is being discussed in several threads over in the DL forum. In brief, the changes are as follows:

Starting March 1, 2013, changes in status miles (not redeemable miles apparently)earned for several fare classes. These apply to tickets purchased after March 1 for DL flights and flights flown after March 1 for partners' equivalent fare classes:

M (cheapest fare eligible for international upgrades with miles or SWUs) decreased from 150% to 100%

F (full fare domestic FC) and J (full fare business class) increased from 150% to 200%.

Starting January 1, 2014 (for earning status for 2015 and beyond) for USA residents/mailing addresses only, either $25,000 spend on a (USA) DL AmEx or meeting spending criteria for elite levels based on fares plus carrier imposed fees (fuel surcharges, etc.) on DL flights, DL marketed flights, and partner flights ticketed on DL 006 stock (not counting consolidator fares, etc.):
$2500 for Silver (FO)
$5000 for Gold (GM)
$7500 for Platinum (PM)
$12,500 for Diamond (DM)