Josh Salmons (an excellent presenter, btw) wrote a good post to your point, Tricia:

The importance of conference rapport

It’s really the ideal – to attend the rest of the event so that you can listen to the other speakers, meet audience members and adjust your presentation based on those data points in advance of your “time on stage.” Seeing what others have said enables a presenter to cut and modify on the fly…but really hard to do that when you pop in and out (as I so often have to do…)

Agree with your point on modifying behavior…ultimately, it’s about motivating them to leave your talk and do something different…but per my comments to Julie…that motivational element has to be sticky enough that it naws at the person’s psyche for severals days until the new behavior kicks in.