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