I like the site. A few notes:

- Running on Heroku is not really an asset security wise. I would put something more significant to ensure users that your site is secure.

- Make sure your site is secure; it will be attacked often and by professionals. Consider hiring an expert.

- The highlighting is kind of distracting and busy.

- You should be able to access some charts and see the going rate without signing up and loggin in.

- What is a Mt. Gox Redeemable code?

- There are laws in most countries that regulate banks in regards to leverage. Have you considered any of this?

- Margin trading is risky and some people will lose more than they bargained for, expect some repercussion.

Best of luck!