I caught this dubbed version on one of our local Spanish channels late at night--it was odd to hear Mickey/Woody Harrelson's drawl rendered in rich, carefully-enunciated, deep-toned Espanol! Since I haven't taken a Spanish class in over 20 years, I only caught every other word, but it made the visuals more integral to my experience.
This is a very, very difficult movie to watch and digest; I saw it in its original release in theaters, I saw the directors cut (I really would have liked to see what Tarantino did with his own script) on video, I've read the original script and the novelization, but I feel that I got a new level seeing it in a language not my own. I recommend catching this, even if you don't speak Spanish! :)
