You might be interested in the results of Media for Democracy's Citizens' Panel rating of the first presidential debate. It is very useful that they break their results down by which candidate respondents favored. While the greatest number (23.8%) of Kerry supporters watched the debate on PBS, 50% of Bush supporters chose FoxNews. In both the Bush and Kerry camps, viewers who supported a particular candidate felt that that candidate's views and approaches came across far more clearly than the others.
I enjoyed the responses of undecided/"other" voters: 46.6% said the debate was extremely useful in helping them understand Kerry's positions, and 40.7% (the greatest number) said the debate was somewhat useful in showing BUsh's positions. 72.9% said Kerry "won" the debate, while 14.6% said Bush took it, and 12.6% favored neither. And over half said that the debate would shape their vote!
On the same page is a link to the "Citizens' Debate Scorecard," where you can register as a citizens' monitor for tonight's debate.