From CQPolitics:

Sen. Blanche Lincoln appears to be on her way to earning the dubious title of most vulnerable Senate incumbent of the 2010 cycle.
The moderate Arkansas Democrat has become a top target of national Republicans in 2010, especially after Sen. Christopher J. Dodd (D-Conn.) announced in early January he was not to going to seek re-election. Meanwhile Lincoln’s weakness at home, which has been reinforced by multiple recent polls, has drawn some of the state’s best known Republicans into the race.
Given these developments and the worsening of the political mood for Democrats, CQ Politics is changing the rating of the Arkansas Senate race from Tossup to Leans Republican.