Post-hook up reality check?

After you have been intimate with someone, do you think their behavior changes? I asked because one of my friends said that he thinks women often pull a bait and switch in dating. The switch comes after they hook up with someone.

I know, breaking news: Sex changes things, right? Is it because we expect different things after we get physical? The guys that I know think they can tell a lot about a woman by the way she acts after sex. What they truly want becomes apparent: relationship or friends with benefits?

Do you believe that after sex, you get a reality check about a person’s personality? In your experiences, does sex change the dynamic in a dating relationship?