What sucks is that while the term Decentralized exchange let imagine the possibility of the elimination of third party risk, actually there is a lot more counterparty risk by using it. (I prefer trust Bitstamp or Cryptsy than a random asset issuer on top of counterparty, and it's not even close).
The thing is, a centralized exchanged like Bitstamp or Cryptsy is really complicated, and you can't read the source. There are potential vulnerabilities throughout their entire systems.
An asset issuer on Counterparty needs only do one thing correctly: hold the asset. They don't need to make sure their wallet software is updated, they don't need to match orders correctly, they don't need to keep orders on the books. They only have to do one thing, and that one thing can be provable (such as providing bank statements, photos of physical assets, etc.). The rest is on the Counterparty implementation, which is open-source.
Do you trust that Cryptsy owns the correct amount of coins for the 50+ coins that they trade? And that a vulnerability in one of the wallets in one of those coins won't lead people to make fake deposits, trade those fake coins for BTC, cash out the BTC and leave Cryptsy with nothing but a bunch of fake coins? (Like supposedly happened with CryptoRush and BlackCoin?)
I'm not trying to pick on Cryptsy here, I use them myself and trust them more than I trust other centralized exchanges. But for them to prove to me that they have all the required coin balances for 50 different coins would be quite complicated. And then they would have to prove to me that their exchange code can't be cheated.