While inarguably President Bush and the Iraq War have become extremely unpopular with a strong majority of the American public, a closer look at the USA Today/Gallup poll numbers doesn't strongly support a conclusion that Bush's new plan had any significant impact on public opinion--either positive or negative.
The USA Today/Gallup poll was based on a sample size of 1,003 and has a 95% degree of confidence in a plus or minus 3% margin of error. The result being discussed as indicating the negative impact of Bush's latest speech comes from the question: "Do you approve or disapprove of the way George W. Bush is handling his job as president?"
Before his speech, the January 5-7 poll reported that 37% approved and 59% disapproved. This latest poll shows a 34/63 breakdown. A one-week variation of three percentage points in his approval rating is within the margin of error and thus not a statistically significant variation. His disapproval rating increased by 4%, making it slightly significant, but not enough to make a big fuss over.
Looking beyond the presidential approval, Gallup has a valuable analysis of their results regarding support for Bush's proposed troops increase. Again, it doesn't look like Bush's speech changed any minds.
Bush's speech did not have a negative, but only a negligible, impact on public opinion. Typically, Bush's public appearances have had the effect of increasing support for his proposed policies, but this one didn't achieve that goal, making the speech's irrelevance the most significant conclusion that could be drawn from these results.