As gw2wiki states, dueling will not be implemented upon release, but may be later.
During Beta weekend 3, I was trying to find ways one could make a "custom match" on a pvp set for him and his friends but all I found was either WvWvW or BG style pvp.
I am not sure why Arena Net wouldn't impement such a feature. One might wish to practice pvp somewhere with his friends... learn how to play, whats effective, whats not.
Being thrown into WvWvW fights or even BG's is chaotic especially for the new players.