I used to play WoW and all i can really tell you about duels is someone challenges you to a duel you can either accept or decline, you cant be forced to accept it. It is entirely optional and as some pointed out its an interesting way to pass time for some. From what I have gathered it seems that pvp for 2.0 is going to be instanced and/or zone regulated too so there's really no reason for "pvp grief" to ever become an issue.