I'm one of the lucky people who have to wait. The airport personnel tells us it's the system that prints out weather information that's out. Not sure why one would want to attack that.
If it is power issues and some bit of infrastructure deep in the back end took a nosedive, wouldn't be surprised if it effects multiple front end systems.
Considering it's an airline, it's likely either a IBM i or a IBM Z System where they track everything relating to their flights (schedules, reservations, checked luggage, etc). A lot of companies (mine included) seem to thing these devices are high-availability giants and never test what happens should they go down. I know if ours ever took a dump we would be in some big trouble (though we could function for at least 24 hours).
Assuming what you've heard is correct this seems to span multiple Delta systems.