I don't believe there's much money to be made with Cex.io. It's honestly seemed shady from the beginning.
There is certainly money to be made. Anyway, just buying and holding will make you lose your money as the price of mining power is sky high. You have to try to buy low and sell higher, and keep the mining profit in the meantime.
You might want to see this chart:
https://docs.google.com/spreadsheet/ccc?key=0AiFMBvXvL2dtdEZkR2J4eU5rS3B4ei1iUmJxSWNlQ0E#gid=0Bitcoin difficulty adjustments there. You should know about those, they will affect the Gh/s market. You have to know what you're doing at least, not everyone will be a winner there. But you can make good money too!