Thanks to DataVeteran's twitter page (https://twitter.com/Datavetaren), I've stumbled on the following link:

https://data.mtgox.com/api/0/bitcoin_tx.php

It shows a bunch of mtgox blockchain submissions. They all include the new transaction ID constructed by Sipa and Krapeles as disussed extensively on the GitHub thread (https://github.com/bitcoin/bitcoin/pull/3656).

Copy/Pasting the NTXID field in blockchain.info gives a series of transactions happening over the course of the past couple days. If I understand correctly this is the testing they announced they would be doing.

Not all NTXID seem to work. This might imply that not all test transactions are going through properly and, thus, the system isn't fully ready for primetime action. If this were the case, the freeze on all withdrawals could be deemed appropriate.