Obama will tell people that McCain didn't want to debate him because McCain is afraid of a debate. McCain will tell people that because Obama didn't want to postpone the debate, that means he doesn't care about the economy. Obama will harp on "four more years of bush / voted with bush 90 percent of the time." McCain will harp on "not ready to lead / painful tax increases."
Both will practically claim that if elected they'll be able to wave a magic wand and fix the US economy, and both will basically say that if the other guy is elected, it will lead the country into complete economic ruin. Both will use their "last word" segments of various questions to drop huge accusations against their opponent that have nothing to do with the question they were responding to, and both will have to use their time on the next question to cry bullshit over those accusations.
I'll watch the debate in disgust, and then I'll hop on factcheck.org and realize that I can either vote for the liar, or I can vote for the other liar.