As a hobbyist musician, the slowdowner plugin for winamp was a great way to learn guitar solos. Hope it makes a comeback.
I generally listen to OTR, audio books, etc., but at increased speed with WinAmp, and other players, but my cheapo Sansa player has a +/- setting that suffices.
I loved the WinAmp TV plugin that would work with an old Hauppauge TV/FM card I have.
For those of us who had to spend uncounted hours rewinding media again and again in an attempt to figure out how to play various songs that we loved and dearly wished to play, it is frustrating when we think of it and how much it would have helped us it were available back then.