I didn't use to, but I started some years ago when I found it made it more enjoyable.

Of course, then I'd go and watch the anime and the voices in my head don't really match the ones on the screen, and then it all gets creepy. For example: I always imagined that Chopper would change his voice when he changed forms... then I watch the anime and the big hulking gorilla Chopper has this little kids voice. It was just weirding me out.