https://github.com/bitcoin/bitcoin/pull/3656MagicalTux commented 2 hours ago
Just to update this thread, it seems that this discussion is mostly stale now. We (at MtGox) will implement this new hash index in our transactions database and start working with it (we will announce a maintenance as we will have to stop bitcoin deposits too during the database schema update) and will start providing this new hash when customers are withdrawing bitcoins, litecoins, or any other coin based on Bitcoin we may support in the future.
We will also provide an API that will allow our customers to use this hash to retrieve the transaction hash as seen in the blockchain once the transaction is confirmed, and will hope others (blockchain.info?) will index this value one day.
We also invite other exchanges and businesses which may need to keep track of bitcoins they send to use this same method, since dealing with multiple variations of the same thing wouldn't be very productive.
If nobody does it, we will also post some test vectors for regular (in=>out) transactions in the near future.