mining right now has the less risk among of all investment, it's really a safe bet, dunno why people can't see this...
i was not talking specifically about poloniex, i only said that there is a risk of insolvence, it may be a low or high risk depending to the exchange. Poloniex is certainly a good exchange, but keeping btc on an offline wallet is certainly safer. A little risk is still present.
That % is not so unreal, on poloniex the medium interest rate is 0.1% a day. There are some bots that claim to reach a 19% interest/year. That interest is referred to btc, not $, so volatility doesn't have anything to do with it.