The price is going down it seems, is it still cheap or was this a one time pump?
If Overstock starts trading their shares on Counterparty platform, there is a high chance that they will issue a OVRSTCK/BTC trading pair and that trading pair would enjoy most of the volume. As far as I know Counterparty allows asset-to-asset trading. CEO of Overstock being invested in Bitcoin and being the market maker for their own shares would be willing to support the price of Bitcoin, and would only need a small amount of XCP for transaction fees. Same would go for buyers of Overstock shares. It's not clear how this would help drive demand for XCP.
the thing is that they do not only want to write a security on counterparty (which I assumed) but use the protocol in a wider way and built a whole front end application. let us see how and in what way they will use xcp. Following the early posts of the core developers, they said that they only get monetarily rewarded by their protocol building in the case that the native currency is gaining traction.
all that being said it is a great announcement for counterparty - do not forget this is little more than 9 months old.