In yeshiva, we used to bet on whether our friends were going to get engaged to a girl they were dating. The spread would usually start off about 50-50, and adjust based on his mood, the length of phone calls, how much he talked to the mashgiach, and how often they were going out, etc.
A couple of guys were so good at it, they paid for all their dating with their winnings.
We later found out they were in cahoots.