The more typical context in which I come across this kind of thinking is when people ask "Do you understand what I'm saying?". Well - perhaps. I can't actually know whether or not I understand what you're saying. I can know of what you're saying seems to make sense to me - but I can't know whether or not my understanding of what you've said corresponds with what you've said.
Much more useful would be for the communicator to ask the communicatee a question - "So, based on what I've just told you, if you encountered what would you do?". This has two benefits: the communicatee is forced to apply their new knowledge, thus helping them to remember it. Also, the communicator is able to gauge from the communicatee's response how well the message has been communicated, and if it hasn't, what needs to be adjusted...
Saying "Do you understand what I'm saying" is just a cop-out, as is what Scoble wrote:
(here commenceth my reproduced comment)
READ WHAT I WRITE, not what you think I write
Sorry Robert, that's not possible. I exist outside of your head; I don't have any way of knowing exactly what you intended to say. All I can do is interpret the things that you did say, based on what I know of the world and the language we're using to communicate.
That said, I'm always willing to admit that my interpretation of what you said was wrong and revise my opinions based on more information from you...
Right now though I'm not sure which of the many things I mentioned above is wrong though, let alone what you actually intended to say.
But - I didn't mention the thick vs. thin clients issue at all - I was talking about one of your other comments that you made just after the link - so that can't be it.
Sorry, I'm really not sure which bit you think I've misunderstood - so I have no idea at all what I'm meant to understand by it :(