Would be nice if they where actually trading Bitcoins.
But that are just Traders
gambling betting against each other. Has as much Effect on Bitcoin as Horse Race bets have on Horses.
I think it has some effect on the real price still. If their odds would tend to differ too much against the real bitcoin price it would become profitable to "arbitrage" their bets against actually buying bitcoins. You could find low/zero risk opportunities where you take a short position on one end and a long position on the other, basically combining odds arbitrage and regular arbitrage.
It can have a very significant impact on the BTC/USD rate on MTGox, much like the trading of derivatives including options and futures can have on the stock, commodity and fiat currency markets. Let us not forget that the market makers on Plus500 and Avatrade have to hedge their positions by trading BTC for USD on MTGox.
I am a client of AvaTrade and find the ability to trade Bitcoin CFDs to be an excellent complement to holding a long term BTC position. This is especially true when taking advantage of a falling market without risking one's BTC and triggering unrealized capital gains on one's BTC.
The ability to trade Bitcoin CFD's is simply a sign of the growing maturity of the Bitcoin market.
