I'm not a fan of sites that are blatant ponzis, and I do question whether or not that is the case here. The returns that they are promising don't really seem realistic given the current Bitcoin mining industry, regardless of whether or not they are operating a "farm" of mining equipment.

I can however speak from experience, and state that CryptoFarm is still paying. I bought a contract a while ago and I am almost fully paid on it. I'm not sure if I will reinvest, however the site is currently still paying.