Never deposit or keep a significant portion of your bitcoin or fiat currency on an exchange unless you are OK with losing all of it. At some point, because of theft, seizure, or negligence on the part of the exchange, you may be faced with losing it all, and you will most likely be powerless to do anything about it.
I agreed with your lesson learn on this one. I will never do any crypto currency trading after my lesson with MtGox. Instead stick with fiat currency trading only, because there are many regulation in placed to keep trader safe.