This is mentioned only tangentially, but how essential are exchanges to the liquidity of Bitcoin today? If most trading is done through exchanges, as opposed to P2P, then couldn't the market be seriously disrupted by DDoSing the primary exchanges (Mt.Gox and the like) for a few days, thus freezing out most casual users and causing a panic?<p>edit: I'm only a casual user myself, so there may be reasons why this isn't a practical concern, but I am curious.