It would really be a great help. Imagine a bot that needs to place orders at certain prices if certain conditions are met but under no circumstances may place the same order twice. Ideally it would look up in its own order list whether its orders are there already (sent but not yet acked or acked and pending or open) or whether they are still missing.

Currently this is not easy: One possibility at the moment would be for my bot to generate an ID and send it in the id field of the signed call and then wait for the op:result that returns this id *and* the official mtgox oid and then update my own database to link these two ids together. But unfortunately the op:result is the only message that will ever refer to this user-generated ID, its the only link between my ID and mtgox ID, if its ever lost for some reasons (temporary disconnect between order/add and op:result during busy times, etc) I cannot reconstruct it. did the order/add goo through? is it pending? is it missing? If it suddenly appears 20 minutes later how do I know where it came from? If I query the private/orders it will not contain these user-generated IDs, I cannot know which of the existing orders belong to which of my bots or belong to manual trading.

Ideally I would want to be able implement a send_order() function in my trading client that is non-blocking and immediately returns an (internal) ID that I can rely on that will survive disconnects, restarts, all kinds of errors, etc. and my cancel_order() function and other order functions would always be able to use this internal ID to refer to the order.

Currently the only reliable way to do it is to encode such additional information in the least significant bits of the order volume: Instead of buying 1 BTC my bot would buy 1.00000042 or + , so each of my bots can recognize their own orders and restore this important part of their state from a simple private/orders query. But I consider this a dirty hack. Its only a workaround.

Such an ID field would not have to be large, people would not need to be able to store their entire autobiography in this field, 32 bit unsigned int would be plenty enough for this purpose.