A consistent 2-4$ BTC price differential has started to be seen compared to other exchanges. Seems more people are withdrawing BTC than the market can absorb. Since Bitfinex lost half it's Bitcoins but applied only a 36% haircut to existing BTC deposits, they are now functioning as a fractional reserve on the BTC side: they can't match 1:1 even the bitcoins people see in their accounts after the haircut. And since Bitcoins are easy to transfer out, they are bound to run into BTC liquidity problems as more and more people cash out. Since they are solid on USD, they will probably purchase additional BTC from other exchanges and drive the price up. This is quite a fragile situation, Bitfinex is in efect short on BTC, a rapid price increase can kill it if they run out of USD to cover BTC withdrawals at inflated prices.