We have recently seen a number of startups (including YC founded AFAIK) that look for ways to make twitter data useful. But I don't remember catching any notice of such successes.

While DataSift realtime capabilities look really impressive, I'm afraid there isn't that much of use-cases to pay for the data mined that way. Even DataSift's own list of possible use cases looks bleak.

In any way though DataSift should be fine with applying their expertise to other sources of data, which doesn't bear the same cost as the twitter's firehose.