See Susskind's Topics in String Theory, 8 and 9.
The main example is String Theory as an extrapolation of the Standard Model.
[One could put a metric on theory-space...
Reverse-engineer the standard model to find the class of Calabi-Yau's that give rise to the particle spectrum...]
Susskind holds that it is not currently possible to find the probability that String Theory is right.
[I disagree, but if it's true String Theory is a trivial extrapolation.]