And I note that since Gox changed their rules about placing orders without actually having the funds in your account (you can't do that any more - so the money is really there), that's even more impressive.
Is it? The total volume of one weekday's trading is around USD 20m.
It should be there. Gox changed the rules effective - I think - April 17th.
AFAIK nothing has been changed yet. The new trading engine was postponed when Gox did their 12 hour unplanned downtime for system upgrades.
The rules change has nothing to do with the trading engine.
TOKYO - JAPAN - April 09, 2013
Orders will only be accepted when there are enough funds available in your wallet!
Dear users, starting on April 17th we will be rolling out a minor change on how people place orders via the Mt.Gox interface.
Until recently, anyone could place a buy or sell order for Bitcoin, regardless of how much funds were actually available in their wallet, resulting in an order showing a "Not enough funds" error status in the Open Orders list.
Starting on April 17th, this counter productive scenario will no longer be possible and will be automatically rejected before validating your order; until you have enough funds in your wallet to match the order value.
While this change should only affect a minority of users, it will however have a major impact on our trading platform and improve our system overall performance.
Regards
Mt.Gox Co. Ltd Team.
https://mtgox.com/press_release_20130409.html