CBS News released a poll this morning, which seeks to gauge the effects of President Obama's Wednesday night speech on health care reform. The poll used a panel design, in which the same respondents are followed-up over time; in this case the same people were surveyed before the speech (August 27-31) and after (Thursday, September 10). Also, the above-linked report provides results for many items separately for those who said they watched and did not watch the speech. In general, Obama's speech seems to have been successful.
ADDENDUM: AARP commissioned an overnight poll of Americans 45 years and older, following the speech. The focus was on how well, in respondents' eyes, Obama addressed their concerns about pending reform legislation.