Right now I'm trying to tidy up my player and this would have helped me immensely had the feature been available.
Although I am fairly diligent with my tagging, I have a number of tracks that bug me whenever I play them because of a problem with the IDx tag of some sort or another (but mostly bad capitalisation). Plus of course, with the tracks I've marked as bad, I now have to work out why they were marked and so on, the timestamp feature mentioned in this thread would have been helpful too.