Facebook started project PlanOut, which is open source environment for projecting and conducting social experiments on-line.
The main idea, which I quote as it is described by authors, you can get through this simple example:
Focus on parameters –
PlanOut is all about providing randomized values of parameters that control your service. Instead of using constants for text size, color, wordings, or a switch controlling the rollout of a new feature, just use PlanOut to determine the value of these parameters. Now you have an experiment.
And more description on release notes: