"SAS 70 Type II or equivalent" is the magic thing to ask for if you want any meaningful results!
Not an accountant, but wouldn´t you need a SAS 55 too, to be sure? Also, from what I remember, isn´t this standard geared towards nonfinancial companies rather than financial organizations? In how far does this apply to MtGox, given that they are based in Japan, given that it is a US standard? What would be the japanese equivalent to ask for?