Joshbb has created an exchange to trade GoxBTC for realBTC - see here: https://www.bitcoinbuilder.com

On there, the bids sit at around 0.6-0.75 and the asks at 0.76-0.8.

Personally I think that GoxBtC are worth around 25%-30% right now - I don't believe they have enough BTC to pay everybody, I think they lost a LOT to repeated withdrawals, especially when you consider that this has been happening since November.