Maybe I'm, just too paranoid, but I think everyone who has physical access to the server on which your site is hosted can read my password out of the RAM if you only hash it once you receive it. and if he/she has my login data he could act as me and legally withdraw the funds in my mtgox account. why not just hash it before encrypting and sending it ?
Solution:
1)Use a unique password.
2)Only put funds in the account which are immediately to be used for trade
3)Don't trade at one time amounts larger than you don't mind losing.
Then, even if they get your password, what do they do - steal five dollars?