In a nutshell
Now you can use Bitcoinica to deposit and withdraw in BTC. We have separated each account into two: BTC and USD. You can trade using any currency as your margin. How BTC account works?
Now you have two accounts: USD and BTC. We calculate your margin balance by converting your BTC balance into USD. You can then trade as you have all your balance in USD.
However, all the profits and losses will be accounted in USD instead. If you make a profit, you can withdraw both BTC and USD back. If you make a loss, you can withdraw neither unless you use part of your BTC to recover the loss in USD.
Currently we don't support conversion between USD and BTC yet. But you can contact us to do so. What does this mean to me?
Now you have a permanent Bitcoin address (accessible in your Deposit page), and you can simply send any number of Bitcoins to this address.
You don't have to rely on Mt. Gox for deposits and withdrawals anymore.
In the unfortunate event that you receive a margin call, you can deposit either USD or BTC and use it as your margin. A word about risk
Using BTC account is a bit riskier than USD account, due the fluctuating value of Bitcoins. You may receive a margin call because of the decrease in value of Bitcoins if your positions are not making enough profit to cover.
Generally margin trading is associated with extremely high risk, and you shouldn't use anything more than you can afford to lose to engage in trading activities on Bitcoinica. Enjoy your trading!
Now you can go to Bitcoinica and continue enjoying your trading. Our spreads have been lowered by half since launch, because of your support!