Just used this this morning. I checked a party of two in online at delta.com (easier to input passport information, etc.), and while I still received numerous warnings that I'd need to check each person in on their individual phone for eBoarding passes to work, I checked in anyway.

Sure enough, each passenger could pull up their eBoarding pass on their individual iPhone once I did this. Worked like a charm.

This is a huge feature-add. Props to the Delta team for including it.

Yes, it still takes a very long time for each step to load in the iPhone app, but at least we're getting very useful new features.