The survey done October 9th and 10th by North Carolina based Public Policy Polling asked 682 voters about their thoughts on Ryan in the midst of the government shutdown. When asked, "Do you approve or disapprove of the job Representative Paul Ryan is doing in Congress?" -- 49% approved and 45% disapproved. The poll also found that Ryan would beat a generic Democratic opponent by just a 50-43% margin if an election were held today.
Opposition to the government shutdown and a generally unfavorable opinion of the Tea Party appear to be driving Ryan's negatives. 59% of those polled opposed shutting down the government to stop the health care law from being put into place. 52% have an unfavorable view of the Tea Party, a group which has strong ties to Ryan.
Once the shutdown is resolved, however, would those negatives still hold up in next year's general election? His last Democratic opponent, whose campaign forwarded the poll to media outlets, believes so. "Paul Ryan stands firmly on the wrong side of this issue. The overwhelming majority of people in Southeast Wisconsin, 59%, oppose shutting down the government. We're only in this mess because Ryan outright refused to appoint a conference committee to work out a budget with the Senate, which was so severe that his party couldn't even pass their own appropriations bills," said Rob Zerban in a statement.
Ryan won re-election in 2012 with 55% of the vote despite doing virtually no campaigning in his home district because he was the Republican Vice-Presidential nominee. That would indicate that only a monumental shift in the attitude of voters in his district would put his seat in play, especially if was actively involved in campaigning for re-election. The poll does indicate however that Ryan has been damaged politically by the shutdown as have Congressional Republicans as a whole, and further political mistakes could make re-election more difficult.
You can see the poll here: