This article does a good job of explaining how betting can be a useful rationality practice. An excerpt:

The interesting thing about this practice was that it made us both think very carefully about the accuracy of all of our statements. The most embarrassing thing ever was to say, "I bet you anything that I'll be on time..." and then be unwilling to back up the assertion with a bet. Failing to bet was an admission that you'd just said something that you had no real confidence in.