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(deindent) Sorry for kibitzing, but I wanted to be fair to all points of view, even those of the dualists. so I tried to stick to presenting the thought experiments without drawing conclusions.

The thought experiment is this:

 you have one observer
 The observer gets cloned into copy 1 and copy 2 (either Hubert/Yorick or star-trek style)
 The copies diverge, either because of internal noise, or because of the environment

From a third person point of view, this is an objective description of the evolution of a physical system, there is absolutely no ambiguity about what is going on- one observer becomes two. If probed, each copy would say that they were the initial observer before the cloning event. But viewed from the inside, if you are the observer getting cloned, there is a very natural question you can ask: Am I going to end up being copy 1 or am I going to be copy 2? This question cannot even be formulated from the outside, so it has no objective answer, but it is subjectively very important if you are the observer.

This scenario is Dennett's (and to some extent Everett's). Since the question doesn't even make sense when formulated in the third person perspective, the answer to this question does not lie in the position and velocities of any atoms. You might conclude that this question doesn't make any sense. But, in any case, the answer to this question is 1 bit of subjective information which both copy 1 and copy 2 know, and which the original observer does not. In the objective third person view, there is no information gained- you know that copy 1 will say ""I am copy 1"" and copy 2 will say ""I am copy 2"".

To give an example of actual OR and SYNTH, I'll go beyond Dennett's example: suppose that the copying goes on indefinitely, so that the cloning keeps happening again and again. Then it is very difficult to say what it feels like for the observer, from the first person perspective. For example, take a star-trek duplicator, and duplicate the observer, and then duplicate each duplicate, but add a twist: the duplicator keeps the data from the first duplication event in its memory banks, and makes a third copy in the exact same state twenty years later, and starts duplicating that observer too in the same way. And then it does so again forty years later, then sixty years later. What is the subjective experience? From a naive counting perspective, I should predict that I would be nearly certainly teleported in time to some distant future point, because the number of future copies of my present state is vastly greater than the two present copies. On the other hand, the total number of observers descended from the current duplicates will always outnumber the observers descended from the future duplicates. So perhaps the right counting is by the number of descendents at each time slice, rather than by the total number of descendents of my present state. Even worse, how can my subjective experience change depending on whether somebody millions of years in the future turns off the darned duplicator? (Boltzmann's brain is a similar idea).  "