List of underrated risks?
As everyone here knows, it would be a stupid idea to switch from airplanes to cars out of safety/terrorism concerns: Cars are a much more risky means of transportation than airplanes. But what other major risks are there that many people systematically undervalue or are not even consciously aware of? The same can be asked for chances.
The rock on top of the computer wouldn't count into the "amount doing the computation". Apart from that, I agree that weight shouldn't be the right quantity. A better way to formulate what I am getting at would maybe be that "probability of being a mind is an extensive physical quantity". I have updated the post accordingly.
Regarding your second paragraph: No, the TV screens aren't part of the matter that does the computation.