Sell on MtGox for 591.18 GBP = 901.73 USD (my account is set to GBP)
That's 70.07 USD profit from 10 BTC, or ~$7 USD per bitcoin traded.
Seems like a good opportunity. The problem is you can't cycle your money quickly, it takes time to sell bitcoin for cash and withdraw it ready for the next cycle.
But I mean there's the potential to make ~8% on each cycle. Buying, transfering and selling should also be a fairly quick process so you're not exposing yourself too much.
I think as soon as instant cash deposit/withdrawls are available through various exchanges these gaps will close up pretty fast.
Even with liquidity being lower you can see them being rather close on the different exchanges.