The NYT weighed in on PA-12 yesterday, and even used "bellwether" in the headline:

Democratic leaders hope that improved economic news will help Mr. Critz, as well as their party nationwide. But that may not be enough to convince voters like [Greene County Democrat Sam] Boyd, who only a year and a half ago was putting up Murtha and Obama signs across Greene County, the southwestern-most part of this sprawling district.

Mr. Boyd’s path to discontent since then traces the bumpy legislative path in Washington, from the auto bailouts to the stimulus plan to the passage of the health care overhaul.

His decision on Tuesday, as well as that of other voters like him in this heavily Democratic district, represents a test of Republicans’ ability to make the midterm elections a referendum on President Obama and the Democratic-led Congress.

A new Public Policy Polling poll shows a dead heat between the two candidates, with Tim Burns up one point over Democrat Mark Critz, 48-47%.

NYT photo. US Sen. Scott Brown and Tim Burns. Tom Corbett is in the middle background.