I don't care about objective minutes:seconds left as much as I care about the percentage of work done compared to how much is left. What I really want to know is that progress is being made and that the process isn't stuck, and roughly how much work is left to do compared to how much has been done. I can make my own extrapolation about time just as well as the program could, and I'd be just as inaccurate. The best progress bars are the ones that stop at some percentage but give you a message saying "this part can take a while, don't panic".