"IMHO, the part in the Discussion section about no usable information traveling backward in time is both unnecessary and wrong.  First of all, I never said anything about anything travelling faster than the speed of light.  And, as for usable information travelling backward in time, read the experimental setup as described on bottomlayer.com (http://www.bottomlayer.com/bottom/basic_delayed_choice.htm).  The whole point is that the ""delayed choice"" DOES change the result of the observation on the primary detector.  It changes the results of an observation made in the past, that is the whole point.  All that nonsense about causality not being violated is a bunch of arm waving.  Prove it.   

 I think that the most interesting result of this experiment, also as described on bottomlayer.com, is this shows the underlying flaws in the copenhagen explanation of the double slit experiment.  As Wheeler observed, an experimenter may choose to know a property after the event should already have taken place.  In other words, as described in the bottomlayer.com explanation, ""the observer's choice would determine the outcome of the experiment – regardless of whether the outcome should logically have been determined long ago.""  Frankly, this DOES violate causality.  I believe this shows that causality itself is an illusion.  QM doesn't care about causaltiy.  This is the direct result of the copenhagen explanation of the double slit expderiment, and it is correct.  Furthermore, Wheeler's thought experiment has been experimentally verified by the results from Kim, et al. 

 So, I think that comment about causality not being violated really takes away from the point of this experiment.  Wheeler was disturbed by the fact that causality seemed to be violated by the Copenhagen interpretation, and Kim, et al. have shown experimentally that this is true.  I think that a lot of leading QM researchers have done science a dis-service by avoiding this issue.  It is a fundamental paradox that has never been resolved.  The more you look at it, the worse it gets.  Copenhagen himself said that he himself did not understand it and anyone who said they did was a liar.  This result clearly makes no sense, yet it can be shown to be true.  But, as long as people go around spouting nonsense like this is only qunatum information which is violating causality and you can't actually do anything with it at the qunatum level is wrong.  It is like sweeping the problem under the rug. 

 While it is true that QM is mathematically bullet proof, it contains at its core this fundamental paradox which no one has ever been able to explain.  I wish more experimental physicists like Kim and others would take this problem seriously and try to understand what is really happening.  I personally think that the so called multi world intepretation is the only way to resolve this paradox, and experiments like this show that any other interpretation leads to crazy results like violations of causality."