I've probably got one of the worst PCs I could hope to render images on, but I don't mind leaving renders running for a few days. What would be useful though is a rough estimate of how long is remaining on a render or detection process. I realise that it would be a bit of a rough guess, but if it was just a rough number of hours, then it would still be helpful.
A secondary use would be the ability to set the software to do something other than play a sound when it's done... maybe turn off the machine or send an email?
At the moment I'm using a ruler and measuring the number of mm the bar advances every 2-3 hours, it's at least giving me a clue. To be honest though once you've got a progress bar it's usually pretty trivial in most programming languages to get a duration estimate - probably simpler even than my ruler based maths!
It may also be useful to give the user an option to see more details of the progress through a given stage. It would be good to have more detailed progress automatically revealed for larger tasks, as these are the ones where the motion of the existing progress bar can appear to stall for extended periods of time.
I've got a larger render to the Blending stage, at which point it's slowed to a crawl, moving only mm in 8 hours. I had a look in windows performance monitor for a while and it's now obvious that each temp file is being read and changed in turn, and given that there are so many temp files, and my disk is rubbish it's going to take a while. If I'd not bothered to open performance monitor though I'd have just quit the process and tried again another day.