I agree that the download was a particularly bad example, but I think the same argument can apply to any progress bar. As a programmer, I always measure progres

I agree that the download was a particularly bad example, but I think the same argument can apply to any progress bar. As a programmer, I always measure progress as the percentage of tasks completed, whether that is bit downloaded, modules installed, mappers finished mapping, etc. The mapper example is actually particularly pertinent. Hadoop's GUI shows me the progress of my M/R jobs with a bar, but it is as dependent on the amount of other tasks running on the cluster as downloading a file is dependent on the traffic in the network. There is no sane way to accurately estimate the amount of time a M/R job is going to take a priori, as far as I know. A stochastic method would be too variable and a method playing clever tricks with psychology seems especially insidious, from an engineer's perspective. You might as well replace it with an "Are we there yet?" button that responds to you in a soothing voice "Not much longer now".