It is "safe" for the most part, especially on Bitfinex due to their size and track record. Lending for margin on exchanges has proven to be a stabe return for some investors and is geared more towards the risk averse who would rather not take a chance in playing with the markets but rather have the opportunity to generate slight gains regardless of whether the market is going up or down.
I would not expect to get rich on margin lending/swaps though.
Well, if OP has 65 BTC and he starts making 2.6 BTC a day (who the hell makes that?), in a month he'll have more than doubled his investment. Then he just has to reinvest again and keep building a ton of BTC. Seems like a good deal to me. Too good to be true actually, even considering the risk that the exchange may run away which is unlikely that you are that unlucky that it happens when you are doing it.
You'll need to get your Bitcoins taxed tho, as far as I know Poloniex is going to require you all kind of credentials, not sure how Bitifinex works tho.