PredictionBook might help with measuring improvement, in a limited way. You can use it to measure how often your predictions are correct, and whether you are getting better over time. And you could theoretically ask LW-ers and non-LW-ers to make some predictions on PredictionBook, and then compare their accuracy to see if Less Wrong helped. Making accurate predictions of likelihood is a real skill that certainly has the possibility to be very useful – though it depends on what you’re predicting.