this goes back and forth, though. iirc, the spread in % terms has been higher than this but i am lazy to confirm. if there is a pronounced crash/downtrend, i think the spread will tighten up substantially.
It has been higher several times, but briefly. Komar made a nifty chart here. https://bitcointalk.org/index.php?topic=432477
On a percentage basis, it's been ratcheting up quickly since the new year.
It might come down to the more normal 10-15% premium, but I've seen posts suggestion that JPY withdrawals and even slow SEPA withdrawals are having problems--we might be looking at the end. Wanna trade your Gox BTC to "GoxUSD" in the hopes of getting 10% vs. the odds of loosing 100%? I think lots of people don't like that bet.