Please remember that day-trading is negative-sum; that is, excluding the exchange, on average people lose.
If bitcoins are considered a currency, I'm not sure this is true, as the system isn't a closed one. Some people will daytrade while others will exchange only in one direction (compared to trading dividendless shares, where the only thing you can do after buying a share is sell it back). Everyone may win, and everyone may lose (except the exchanges, which always win).
If the one-direction traders are included, it is definitely negative-sum. The speculators can only win if the one-direction traders lose.
Why? Let's assume I have € and I want to buy something in $ because it is cheaper (quite a common scenario, when hardware vendors tend to sell something at $99.99 in the US and 99.99€ in Europe, when 1€ = $1.3), even when I include the currency exchange fees.
In the end, I may be very happy and have made a good deal by having exchanged my € for $, while the person doing the reverse transaction may be happy because he made a good deal in selling his $ for € at a better rate than in bought the $ initially. This is a win-win, both for me and for the speculator.
Why is that so? Because the hardware vendor is not included in the loop, he does not explicitely use an exchange. He will use the $ to pay his employees in the US, and the € to pay his employees in Europe. He may convert some $ to € or some € to $, but that would be small fraction of what he earns.
