They bought Bluefin (biggest acquisition pre-IPO) which did a ton of really great sentiment analysis. They ended up shelving Bluefin's product (which was targets at brands and TV networks), because they'd already signed a deal with Nielsen. A shame too. Bluefin's data was amazing. And they had lots of paying customers.

It could be a very easy add-on play for big users, but Twitter hasn't historically wanted to be in the services business.