What types of activities permit joinder of multiple co-defendants in a single patent case?

In recent months (perhaps due to the enactment of the Leahy-Smith America Invents Act) many courts have been taking a close look at the joinder of multiple co-defendants in a single patent case. In particular, many courts have been exploring the different types of activities that might qualify as a common transaction or occurrence sufficient to support joinder. This list provides summaries of recent court orders addressing various challenges to joinder of multiple defendants in patent suits.