Bush's best performance so far, though SNL will skewer him for the frothing mouth. He also did the best job so far of explaining why Iraq is so important. Finally, as Richard has pointed out, he nailed Kerry on his Gulf War vote. On the other hand, he still looks and sounds goofy at times.
Kerry is clearly much less comfortable and confident when it comes to talking about social issues. You could seem him stumbling around on the abortion, gay marriage, and affirmative action questions. Also, he never put Bush on the defensive as he did in the first two debates. Still, the focus on jobs and economy doesn't help Bush.
I call it a tie, maybe a slight edge to Bush.