|I have had two different cassette players that I listen to unabridged audio books on. They have two slider controls. The first controls playback speed from 0.85X to 2.0X. The second controls pitch from 1.0 to 2.0. The speech is slightly clipped at the 'less chipmunky' setting but not terrible.
They work well and are very useful in the right circumstance.
With speech only, I agree that this could be a benefit, but speech is all about the words (obviously, heh). Personally, I use a Rio 500 with Audible; I don't know if I'd ever use this feature if I could, though.
With a TV show or especially a movie, there's a lot more going on that the director is displaying for you. The movement especially would annoy me. I kinda like to watch things as the director intended, and physical movement at 1.5X or faster would distract me. I just can't figure out the appeal.
Mind you, most of my viewing (75%) is DVD and HD programming, so maybe I'm just being anal about it, but the rest is either hockey during the season or the odd sitcom like "Coupling".