Fairly new to bitfinex but a long time lurker 
That's madness, it implies at least a 25 times gain in bitcoin price per year.
That's madness, it implies at least a 25 times gain in bitcoin price per year.
Which year did it not exceed that?
Past performance does not reflect future returns!!
Even if bitcoin were to gain as high a market capitalisation as gold its price per coin would be about $120,000 a piece, realistically in the most optimistic example inn the next 5 years it could maybe make 10% of this at very most.
This implies a fair price at the end of those 5 years of $12,000 now lets say it doubles that due to fluctuations which a trader could take advantage of that's $24,000.
Lets just run the 25 time the current price (mtgox) $1000 is $25000.
In other words this five year crazy optimist scenario already stretched to double the most optimistic price would have to happen in a year to have the trader come even close to breaking even.
So when you stack assumptions on top of assumptions, it doesn't add up? That's pretty convincing.
Besides, you are forgetting that most bitfinex positions are short term, so they only have to beat the interest rate for the duration of their trade.