[quelsolaar]

Most users don't understand that making an accurate progress bar is incredibly hard, for most tasks. Is not very intuitive, but once you start looking in to it you realize that almost nothing in a computer is deterministic. Task switching, cashes, file system buffers, disk fragmentation, variable clock frequencies, and loads of other factors, make the speed of a computer very hard to estimate.

I do favor progress bars that say things like "you have downloaded 47% of file X", because its a statement of fact, not an estimation of future performance.

[WorldMaker]

Progress Bars are the most user visible insight into The Halting Problem that our entire industry has. In so many cases, if we knew exactly how long things would take to compute we'd have already computed them or we'd have a world bending solution to The Halting Problem that would change everything. It's really hard to describe NP Complete/NP Hard to the average user, and it shouldn't be a surprise that the poor tool that keeps having to do it over and over again in so many places and ways, the lowly progress bar, keeps getting blamed for our industry having failed to solve (and unlikely to ever solve) The Halting Problem.