not with poloniex, really hard to have insolvency with their monstrous volume, they are the first lending platform also for bitcoin, but the percentage you are talking about are no where near the reality, where do you get high % like that with the volatility of bitcoin?
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.