The graph below compares the NBC poll with positive sentiment on Twitter. The data was collected between Dec. 27 and Dec. 30, 2011. One might note that the surprise finish by Santorum was "predicted" better by Twitter activity than by "scientific" polling.
In research Global Point has done in the past, its data tends to be about two weeks ahead of polls. Social signals and polling
The Twitter "positive" activity indicated that something was going on, that Rick Santorum was fast gaining traction.