I disaggree, you can indeed make profit in cex.io. Its more like an exchange where your shares pay dividend each day.
Assume you buy 1GHS today @ 0.0075BTC.
1GHS makes approx. 0.00003736 BTC/day in today's difficulty. Taking maintenance fee into account:
fee is $0.26/month for 1 GHS
which makes 0.26/660 = 0,00039 BTC/month
which makes 0.000013 BTC/day
So this leaves about 0.0000243BTC/day.
There's also a 0.2% trade fee.
So in order to stay profitable, you could either sell the 1 GHS today for >0.007515 (0.0075 + 0.2%) BTC, or tomorrow for >0.0074907 BTC, or after 2 days for >0.0074664BTC and so on.
Of course these figures will change after each difficulty adjustment, but logic stays the same.
The way I see it, the only thing that makes it a risky investment is the possibility of a website hack/shutdown etc. (think mtgox) since all the coins/ghs are online.
When your shares start producing negative value everyday, your entire plan goes out the window. Now your "shares" are losing money every day, and the price of "shares" would have to skyrocket well above what you spent to compensate for the fact they essentially have a lean against them.
Your buying gh/s, that should only decrease in value (cex.io doesn't add new hardware for you, like they should in this type of model), the "shares" are losing value by mining with that ghs, and you are expecting to profit somehow? Thinking you can make profit on cex.io is the same as thinking your going to buy a brand new car, drive it off the lot, and sell it later for more than you paid, can it happen, yes (maybe the ford gt or something), is it likely, no.
