EDIT: This particular site does margin trading differently to how I thought margin trading normally works. So... disregard everything I just said?

Bitcoin economy and a possible violation of the efficent market hypososis. With the growing maturity of the Bitcoin ecosystem, there has appeared a website which allows leveraged trading, meaning that people who think they know which way the price is going can borrow money to increase their profits. At the time of writing, the bid-ask spread for the rates offered is 0.27% - 0.17% per day, which is 166% - 86% per annum. Depositors are not actually trading themselves, so the only way failure modes I can see is if the exchange takes the money and runs, if there is a catastrophic failure of the trading engine, or if they get hacked. I Gwern estimates that a Bitcoin exchange has a 1% chance of failure per month based upon past performance, but that was written some time ago, and the increased legal recognition of Bitcoin plus people learning from mistakes should decrease this probability. On the other hand the biggest exchange MtGox froze withdrawals a few days ago, but note that they claim that this is a temporary technical fault.  As additional information, Bitfinex's website states "The company is incorporated in Hong Kong as a Limited Liability Corporation.", which would seem to decrease the likelihood of the company stealing the money. In conclusion, even assuming a pessimistic 1% chance of failure per month I reach a conservative estimate of 65% APR expected returns (assuming that the interest is constant at the lower 0.17% figure) . So why aren't people flocking to the website, starting a bidding war to drive the interest rate down to a tenth of its current value? Unless there is something wrong with my previous calculations, the best explanation I can think of is that it simply has not generated enough publicity. Perhaps also everyone in the Bitcoin community is assuming the price is going to increase by 10000%, or they are looking for the next big altcoin, or they are daytrading, but either way a boring but safe option doesn't seem so interesting. In conclusion, this seems to be an example where the efficent market hypothosis does not hold, due to insufficent propagation of information.

Disclaimers: I don't have shares in Bitfinex, and I hope this doesn't look like spam. This is a theoretical discussion of the EMH, not finanal advice, and if you lose your money I am not responsible. I'm not sure whether this deserves its own post outside of discussion – please let me know.