For other (potential) MtGox -> BitInstant users:
If you plan on using BitInstant to transfer funds to MtGox, be extraordinarily careful that you triple-check the account number you enter--including the number of numerical digits, capitalization, spaces or other non-printing characters and character set (ASCII vs. Unicode). MtGox has changed the format of account numbers without warning before, and neither BitInstant nor MtGox has taken responsibility for "errors" that resulted from this with any consistency.
In early April, MtGox changed the account number format from a 6 digit number to M+(2 new digits)+(6-digits)+X. BitInstant modified the text on their interface page to indicate that the account number format was "M..X". However, they did not indicate the number of digits and they did not change the underlying code to reject entries in the older 6-digit account number. (To the best of my knowledge, they still have not made this change as of June 1.) Some users, including me (CryptoVortex) and srsizzy, entered M+(6-digits)+X. If you are another user who experienced this problem, please contact me.
The important point is that the net effect of this was that some users (including srsizzy) did eventually received the funds, while others (including me) never will. After literally dozens of emails to support at both companies, the net result is that each is pointing the finger at the other. There appears to be a large black hole between MtGox and BitInstant. I'm not just talking about a black hole in cyberspace, but also in the business and legal worlds. In my opinion, neither company provides adequate warning; certainly they do not collectively provide all possible protections against, and accountability for, disappearance of funds into that hole. If your funds should find their way into that hole, they will have plenty of company.
We cannot always take responsibility for user error. Take for instance a customer inputing a wrong btc address that is still valid. Bitcoin transactions are designed to be irreversible. We send your funds where you ask us to send them. On some level the user needs to be responsible for understanding what they are doing and filling out the correct info on their order.
This is a similar situation with Mt.Gox. We provide customers with examples of the correct format and warn them to triple check their orders. We send your funds where you tell us to send them. If you send to the wrong Gox acct. then Gox will tell you that they cannot move the funds without proper documentation due to Japanese regulations. I realize that Mt.Gox is telling some customers to contact us for resolution. However, if the funds are sitting at Gox and we cannot move them then how can we realistically help? At the end of the day we no longer have your funds. They are at Gox. We would love to help but it is simply out of our control. Mt.Gox used to help us re-route funds on orders where the customer put in the incorrect info. Now they do not.
If you had gotten caught up in the MX account number change then that should of not effected you order. At that time Gox was still willing to help us with these orders and correcting where funds were sent. Also, sending to an invalid Gox account may not send your funds anywhere and we can usually correct these problems. But when a user sends their funds to a valid account that does not belong to them then it's a problem. Why? Japanese regulations does not allow Gox to move these funds so easily.
We sympathize with customers in this situation so going forward we will be offering customers effected by this issue discounts on fees with future orders thru BitInstant at new.bitinstant.com. We are also working to upgrade our systems so they will not allow a customer to make errors on their order.