I actually started with 10 GH/s on PBmining back in mid-2014, last time i checked, i made profit. Websites like PBMining are just Ponzi, same ponzi but different system, instead of sending bitcoins to address and waiting for others, you just send to your account on these "cloud mining" websites and wait for the website to die slowly, you'll get your bitcoins until that happens so; Ponzi. Never.
You can just exploit it by participating in its giveaways and whatnot, just don't dump shittons of money into it. You can put in a bit just when it starts, since the ones who start in a Ponzi will nearly always be the winner.