Charles Franklin studies it:
Gingrich’s path is somewhat different [than the Bachmann, Perry and Cain surges]. His recognition levels have remained at the top of the field, along with Romney’s, at 80-90% with only the slightest of upward trends. This means none of the Gingrich favorability trend is due to new-found visibility, as it is for all the rest save Romney and (to a lesser degree) Paul. Rather Gingrich’s trends show that even as a well known figure public affect for him is uniquely variable.
The Dish 