This is ok but it would be tremendously better if unbacked orders would be deactivated rather than cancelled, so they become automatically active when more funds arrive. And the backed part should remain active - e.g., if you put a buy for 100 shares but can only afford 30, you'll have an active order for 30 and unactive order for 70.
Just like on Mt. Gox.
Further improvements will be made on this over the next week or two.