This is a good AP article on the coming VP debate: Palin, Biden a lively pairing for veep debate. It says that some Democratic strategists are actually worried about Palin after seeing her 2006 gubernatorial debate, which is circulating on the web. (I haven't seen it yet.) In Alaska, she had some of the same problems that she's having now: she was considered a lightweight, and she offered banal generalities in response to questions about education and the state legislature. At the same time, she had more understanding of energy issues. But, through all of this, she managed to impress the voters with her style, conviction, wit, and charisma. These things have won the day with others, as they did with Reagan in his 1984 debate with Walter Mondale.
The description of Biden actually made him somewhat likable. When Biden was running against Senator Cale Boggs in 1972, he knew the answer to a question about a genocide treaty, whereas Boggs did not. Biden pretended that he didn't know much about it either, since rattling off his knowledge would humiliate Boggs, whom many saw as the family's favorite uncle. Biden wrote later that he had a lot more political sense back then than he has today.
It will be interesting to watch.