Looks like you can opt-out of the relay service. From the very bottom of the art...

		gooderlooking on May 27, 2013 \| parent \| context \| favorite \| on: BitTorrent Sync Is A Dropbox Killer, Or Maybe Much... Looks like you can opt-out of the relay service. From the very bottom of the article: Traffic Relay ... You can opt out of this, but it could result in peers not being able to network with each other.