Stan Greenberg and James Carville have released a new strategy memo based on recent polling conducted in the 45 most competitive Republican-held House districts. The full memo is here (pdf) . Full poll results here (pdf) . Those crunched for time can get the gist of the findings from Carville and Greenberg's concluding paragraph:

Democrats are winning the 15 most competitive Republican-held districts by a 3-point margin and have the opportunity to expand their lead further if they develop a sharp critique of Congress. Clearly, this election could break further and most likely for the Democrats.