Playing with music off is one thing (and yes, many people prefer to listen to their own music while playing), but playing with the sound completely off seems like it would be tough -- there are a lot of audio cues going on in the game, and with sound off, you might not notice that a party member accidentally pulled another mob offscreen, or that someone behind you is casting a certain spell, or any number of other things that have specific audio to them. That doesn't need to be the only thing you listen to (I usually have to turn down the game sound during raids, just so I can hear what's going on in Vent), but surely listening to game sound makes you a better player.
Do you keep the sound muted all the time, and if so, why? And do you have any trouble playing if you do? Of course, it does help you avoid that annoying PW:S sound, but as someone who keeps the game sound up (though not the music), it seems like there are specific cues meant to be heard while playing the game. Don't you miss those with the sound off?