engine - 4:40 pm on Jun 13, 2012 (gmt 0)
I can only cite one example I know for a fact has helped, and it's a support service. As soon as the company receives a comment, sales request, complaint, or request for help via twitter it reacts immediately and works resolving the issue with an up-sell. They told me that a good number of complaints turned into satisfied customers returning to buy again. The up-sell was the key. simple example, "If you're buying widgets, don't forget your batteries."
There's one thing it's hard to beat, and that's customer service. Twitter's platform is so instant.