Patch 4.0.6 is being deployed on the PTR servers starting today, it looks like. We have confirmed reports of it from some trusted individuals (and MMO-Champion has already got its hands on the client files), but the actual client is not able to be downloaded from the website yet. We think if you have a previous PTR client, you can update that to the latest patch and check out the changes.
As for the changes themselves, right now, indications are that they are a lot of the tooltip changes and other minor tweaks prompted by the last month of hotfixes. Remember that just because a change goes up with a hotfix, a lot of times, the in-game wording won't be able to be updated until a client patch.
And just to be super-clear: This isn't patch 4.1. There are no indications that there are any new raids or anything else with this patch.
More throughout the day as we get it in!