Okay I've read the whitepaper. The only thing that really concerns me about the Decentralized Exchange is that though I see no current flaws in it, there may be ways to sort of abuse it.
In the end I see one of three ways abuse would be attempted:
1) [John claims he did not receive $200 but actually did. John declines.]
John = +$200, -2.1 NMS
Jenny = -0.1 NMS
2) [Jenny claims to have sent $200, but actually did not. John declines.]
John = -2.1 NMS
Jenny = -0.1 NMS
3) [Jenny claims to have sent $200, but actually sent $100. John either accepts or declines.]
This is a mutual destruction scenario in which some interesting game theory may end up coming into play.
3a) John declines (mutual destruction)
John = +$100, -2.1 NMS
Jenny = -$100, -0.1 NMS
3b) John accepts (John realizes that either way he will lose 2 NMS but this will save him the collateral 0.1 NMS)
John = +$100, -2 NMS
Jenny = -$100, +2 NMS
The way I see it is that John and Jenny don't know each other since only their addresses would be shown. Therefore there would be no reason for them to stab each other in the back. Plus there's collateral which means if Jenny tries to stab John in the back she'll be losing out money or NMS.