Here are Sarah Palin's daily approval numbers from the Daily Kos/Research 2000 tracking poll:
In the span of five days, Palin has gone from +17 to +4 -- a statistically significant shift. This includes the Gibson interview as well as the media's sudden focus late last week on the Palin/McCain lies. In comparison, Biden is at 48/32/20, Obama is at 54/38/8, and McCain is at 51/45/4.
So Palin may not be the least popular of the four -- McCain is, but she is certainly the least liked of the four candidates, and given that both Obama and Biden are at +16 favorability, McCain's +6 and and Palin's +4 point to a fundamental weakness that will likely play a role moving forward.