During the month of January, Gallup has been conducting 1,000 interviews nationwide each day for their tracking poll following the nomination races. The result given for a particular day includes the interviews conducted on that day and the preceding two days. (Check out the Gallup site for more on the methodology). In other words, the figures given for January 30th include interviews conducted on the 28th-30th.
This provides a good picture of the dynamics of the races heading to Super Tuesday. But keep in mind, this is a national poll, and a little less than half the states will be voting on Super Tuesday.
The Democratic race has tightened considerably during the past few days. The most recent numbers include two days during which Edwards was still in the race and yesterday's interviews, which were conducted when he had announced he was leaving the contest. It is too early to see how his exit is affecting the support for Obama and Clinton, but the contest for the Democratic nomination is clearly neck-and-neck.
The Republican nomination race, on the other hand, is shifting significantly in McCain's favor.