I was talking to a friend w DL marketing on Saturday about how they have been doing better with their Twitter presence in the last year or so. She said @DeltaAssist is handled by reservations agents for the most part, which explains how they are able to respond/act on customer issues so quickly. Some companies use PR people to monitor Twitter, those that use customer service agents typically can respond more effectively to customer issues. (Comcast & AT&T are others I have used & found faster/more effective than a phone agent)

Coincidentally, an article in this Sunday's AJC covered much of what we had talked about:

http://www.ajc.com/business/fliers-in-a-fix-980537.html

For example:
Delta started the @DeltaAssist Twitter account in May 2010 after monitoring social media and realizing that customers were talking about Delta, “but we weren’t in the conversation,” said Delta spokeswoman Susan Elliott.

Since then, @DeltaAssist expanded to a 24-hours-a-day, seven-days-a-week operation run by 12 “social assist” agents to address problems in time zones around the world. While many companies have marketing handle their social media, the employees who handle the Twitter account for Delta are from reservations, bringing their customer service experience.