Do you expect to be exclusive after the first date?

My roommate & I are on opposite ends of this subject. I don't see anything wrong with playing the field. If you're officially in a relationship, then I understand, but dating to me doesn't automatically mean exclusive.

She says she expects to be exclusive immediately & she can only date one guy at a time. If she finds out after one date that he is talking to other girls, she'll block him.

I guess everyone's definition of dating is different? How do you feel?