You have not explained how it is their incompetence yet.  I understand your frustration, $4,000 is not a small amount to lose.  However, they are probably not to blame.  Do you reuse your password in multiple places (including any pool you mine at).  Is it a strong password?  Does anyone else know it?  Are you sure you don't have a keylogger or any other form of spyware?  MtGox can only do so much to prevent unauthorized access, the rest is up to you.