I second Botolo86's reply! cex might have the real fancy site and the picture of "their" equipment but that doesn't make them legit! I've been with PBmining for over two weeks, they've been ready to respond to my questions when I had issues and they pay out on time and correctly!!! Love them! If they where to pull out on us it'd really really really hurt me but I have no thoughts that I'll have to worry about that! You ask CEX to take a time stamped picture of their rigs and an employee or two and see what kinda answers you get from them I'm sure it'll be the same!
What I also meant to say is that in this Bitcoin economy, everyone is a small player and companies grow up one day after the other. If I put my money into Bank of America, I know that if anything happens I will have my back covered. If something really bad happens, I will sue Bank of America.
If I put my money in CEX, PBMining and any other similar company, if things go belly up see if you can sue them. Most of these companies are not in your same home country and you don't even know their real business name. CEX could tell you tomorrow: "sorry we have been hacked and they stole all of your bitcoins", or they could just shut their website down. Same thing with PBMining.