I took my son's cub scout troop to the local fire department a few years ago. They had a camera smaller than a shoe box that did thermal imaging - it could see foot prints left through shoes for a few minutes. They use it to find hot spots in the walls after fires, and talked about lending it to the police in hostage situations to determine where people were holed up.

One HUGE problem with this idea is that it will really screw up people who have to work on multiple computers. It also greatly magnifies the cost of a (whole) computer upgrade - the users will have to retrain the interface. (having an easy method to transfer settings would be a possible work around for this)

Also, what is right for one person is wrong for another. Think of all the tech support people who go to other's computers. Using this idea, each computer is going to be different, making them look ignorant because they are reading the entire menu instead of knowing where in the list the option is located. Also, the tech-support activity will change the interface, making it harder for the user to start working again.

Going to a real-world example, I have a father-in-law who hates computers. One reason is that they do not have a consistant interface. He actually gets mad at everyone who comes in to "fix" his computer because they always change the interface. In his case, the reason this is such a big deal is that he only uses the computer once a month, and it means that the directions he wrote in the notebook no longer work.