Okay, I will take the other side of this.
I think the three day rule is effective if you are seeking a certain personality type. A woman that can't wait 3 days to hear from someone that they just met may be way needier, high maintenance, and clingier than a man may want to start a relationship with. If you are looking for a reasonable women who isn't ready to jump into an instant commited relationship (stalkers) then this is very effective. These type of women are usually attracted to a man who has some aloofness and mystery. Waiting more than 3 days can send the wrong message that you don't care or only want a booty call.
Also, you can warn her about being busy and you may not call for a couple days when you receive her number. If a girl can't wait 3 days how can she make a commitment for life anyway?