Ok I think I understand your point that XCP-invalid-TX spam cannot be filtered at the point of origin like invalid BTC transactions and a motivated attacker could spam the network to make it extremely slow to use XCP.
I think this is a valid concern, even if somewhat mitigated by the 0.0001 BTC transaction fee. I'll post this to the BTCTalk thread and see if someone smarter than me has an idea to defend against it.
Here are a couple of uses cases off the top of my head. This is by no means comprehensive.
* The ability to issue shares in your company/startup and have them be traded from Day 1. Unlike BTCT/BitFunder/Havelock, Counterparty is a P2P protocol and cannot be shut down by regulatory agencies. Kind of like BitTorrent.
* The ability to trade XCP for Bitcoin and vice versa without relying on any fallible counterparty. There is no centralized exchange to steal money from you or fail like MtGox. There is no escrow required to trade with peers because Counterparty guarantees atomicity of transactions.
* The ability to place a variety of different bets. Currently the protocol has support for simple contracts-for-difference (CFDs) and binary Equal/NotEqual bets. Why is this useful? You could for example hedge your exchange rate risk completely by being short a XCP/USD contract. This allows you to hold your wealth in cryptocurrency but have no exchange rate risk. Another use case is sports betting. There was a friendly bet on the Super Bowl, for example.
Could you give an example of a double spend attack on XCP?
From what I understand, XCP transactions guarantee atomicity and funds are swept from addresses to fund any bets/orders immediately. The risk of double-spending XCP is the same as the risk of double-spending BTC as XCP relies on bitcoin's proof of work.