When did this happen? Did you use the same password on multiple systems? Did you use a crappy short password?
I'm not trying to 'blame the victim' here - but in most cases it does seem to turn out that the user was using woefully inadequate passwords, or that the security breach was on the user's side, so please let us know if you have any information on how your 'account was hacked'.
Also - there is a daily withdrawal limit in place on most mtgox accounts.. are you saying that all 300 or so disappeared at once - or that this happened over a period of time?
How much followup have you done with mtgox support?
I see you've made another thread regarding this: https://bitcointalksearch.org/topic/newbie-experience-with-mtgox-54711
Please reply there.