I'm going to repost my reply to zhoutong, as this thread became temporarily derailed and I don't want him to miss it:
@zhoutong: Thank you for the concise reply to my concerns. Having bitcoinica around still worries the heck out of me, but I am very glad it is you who is running it. You seem like a trustworthy guy. I hope you do not let us all down.
Since you won't/can't open your order books for the reasons you outlined, then would you consent at some stage to regular independent third party auditing of your accounts and your platform?
I would consider this option, but it's quite expensive.
Most brokerages don't open their books too, I know a few brokers who trade against their clients. (They told me secretly, LOL.) The forex market is so big that hardly any broker can run the stops himself. The only way for manipulation is to manipulate the market making price. That's why the number one assessment of a brokerage's reliability is the accuracy of the prices.
When Bitcoin gets larger (it's necessary to go to $100+ to get "larger"), Bitcoinica will no longer be a factor for instability.
I feel that there's no need to outdo a forex brokerage. If everyone gets third party for auditing, they will all miss a huge selling point - price accuracy.