Don't believe it.
Much of the Old Media has been trumpeting a Newsweek poll showing John Kerry gaining a narrow lead over W since Thursday night's debate as if it were the revelation of the Ten Commandments on Mt. Sinai. However, a Power Line Blog article describes how the sampling changed between the previous Newsweek poll and this one.

UPDATE: Reader Meg Kreikemeier points out that according to RealClearPolitics, Newsweek's most recent poll included 345 Republicans, 364 Democrats and 278 independents. This compares to Newsweek's published data for their most recent prior poll, which showed President Bush with a comfortable lead: 391 Republicans, 300 Democrats and 270 independents. Yes, if you drop 46 Republicans and add 64 Democrats, you will get considerably better results for the Democratic nominee. This is a good reminder of why poll data always need to be taken with a grain of salt, especially until you see the underlying data.

Now I don't know what ratio of Republicans to Democrats is a most accurate sample of the nation. However, it is obvious that if you change the ratio by as much as was done between these two polls, you are going to show an apparent Kerry 'surge' regardless of the debate outcome or any other circumstance in the real world.

UPDATE: Also, check out the intriguing clip of video linked from this Drudge article on John Kerry's actions during the debate.