[derefr]

With a process that happens on regular intervals like a Windows Update, I always wondered why the system doesn't store metrics on how long the process has historically taken on previous runs, and then just uses a weighted average of historical times as a time-based total estimate, converted into a divisor for work-based progress estimates (i.e. if previous runs took 60 minutes on average, then progress at 25% would say "45 minutes remaining", then if it suddenly jumped to 50% would immediately say "30 minutes remaining." Even if they're choppy, those time estimates would actually be correct if you sampled and averaged them.)

[snupples]

Not sure if anyone's mentioned this yet, but the old original Mac OSX boot screen had a progress bar that was based on the exact length of the previous boot time.