"I would like to know whether it is likely to rain tomorrow. However, when I ask an Everett follower, all she will tell me in direct response to my question is that `it will rain and it won't rain.'
Nevertheless, she is willing to tell me whether or not it is rational for me to take an umbrella. I suppose that if she tells me that it would be highly irrational for me to take an umbrella, I can take the hint and deduce that it is very unlikely to rain.
However, there does seem something wrong with the fact that she is not allowed to say this directly."
Robert Wald reviewed Many Worlds?: Everett, Quantum Theory, and Reality