However, there was good news in the poll for Republican vice presidential nominee , too. Palin's debate performance improved uncommitted voters' perceptions of her overall, and on a number of specific measures. But uncommitted voters still have doubts about her ability to assume the presidency if necessary and she lags behind Biden on her knowledge and preparedness for the job.
Few of the pre-debate uncommitted voters committed to a candidate immediately afterwards - about seven in 10 remain uncommitted.
Voters' interest in this year's vice presidential debate was high before the debate - about as high as interest in last week's presidential debate.
Immediately after the vice presidential debate, CBS News interviewed a nationally representative sample of nearly 500 debate watchers, assembled by Knowledge Networks, who were "uncommitted voters" - voters who are either undecided about who to vote for or who have a preference but say they could still change their minds.
Forty-six percent of these uncommitted viewers said Biden won the debate Thursday night, while 21 percent said Palin won. Thirty-three percent thought it was a tie.
Even a quarter of Republican uncommitted voters thought Biden won the debate.
Among these voters, there was improvement in views of both Palin and Biden. Fifty-five percent of the uncommitted voters said their opinion of Palin had changed for the better as a result of the debate; just 14 percent said they had a lower opinion of her after tonight, and 30 percent said their views of her did not change.
As for Biden, 53 percent of uncommitted viewers said their image of the veteran senator improved, while five percent said their opinion of him got worse. Forty-two percent said their opinion did not change.
Palin's rating improved after the debate on being knowledgeable on important issues - from 43 percent to 66 percent - but Biden still far outpaces her. After the debate, 98 percent thought he was knowledgeable.
Uncommitted voters' views of Palin's preparedness for the job of vice president also improved as a result of her debate performance - from 39 percent to 55 percent. But those numbers are still nowhere near the percentage that thinks Biden is prepared - 97 percent, up from 81 percent before the debate.
Men were more likely than women to think Palin is prepared for the job, but that's not surprising, as more men tend to be Republican than women.
Although Palin made some gains on perceptions that she could serve as president if needed, she rose just nine points on that measure after the debate, to 44 percent. In contrast, almost all uncommitted voters think Biden would be an effective president.
One of Palin's strengths has been her ability to connect with voters. Before the debate, 58 percent of uncommitted voters felt she shares their values; that rose to 73 percent after the debate. Fewer uncommitted voters said the same about Biden either before or after the debate.
Debate watchers who thought Biden won the debate cited his knowledge and experience - especially on foreign policy - often using words like "knowledgeable," "experienced" and "articulate." Others mentioned his sincerity and compassion, and mentioned finding out about his family life - particularly that he was a single parent. In contrast, they felt that Palin was overly rehearsed and dodged answering questions.
Debate watchers who thought Palin won the debate praised her style. They saw her as "outspoken," "determined" and "on the ball." They also said she was more intelligent and accomplished than they expected, echoing the finding that 66 percent thought she was knowledgeable in the post-debate poll.
Uncommitted voters include those who say they have a preference, but also say they could still change their minds. Eighteen percent said they were committed to Obama, ten percent were committed to McCain and 71 percent of these voters remained uncommitted after the debate.
Read the complete poll (PDF)
This CBS News poll was conducted online by Knowledge Networks among a nationwide random sample of 473 uncommitted voters - voters who don't yet know who they will vote for, or who have chosen a candidate but may still change their minds - who have agreed to watch the debate. Knowledge Networks, a market and public policy research firm based in Menlo Park, CA, conducted the web poll among a sample of adult members of its panel, who are provided web access if they don't already have it. More technical information is available at http://www.knowledgenetworks.com/ganp/reviewer-info.html.
This is a scientifically representative poll of uncommitted voters' reaction to the presidential debate. The margin of sampling error could be plus or minus 5 percentage points for results based on the entire sample.