We had a fairly conservative cross-validation function that tested the results of the genetic optimization for a first pass.  Following that, Omnivore was put into "observation" mode, so we could verify that the results it generated were predictive going forward, and not just biased towards the test set.  Over the course of the past few months, the model has held up quite successfully.<p>Since accusing a customer of being a spammer without non-heuristic proof can be an emotion-ridden experience for everyone involved, we were conservative and optimized for accuracy over efficiency pretty much every step of the process.