Excited to jump in on the Icecrown Gunship battle today on the PTR? Too bad -- Daelo has posted on the forums that due to instance server issues, today's testing has been canceled. He posted that on the EU forums, so we're not sure if that means it's also canceled on the North American realms, but we'll presume so. If we hear otherwise (as this is the PTR, all testing and data is subject to change at a moment's notice), we'll let you know.
As for what this means for the testing cycle, probably nothing at all -- delays and changes are pretty standard for the test realm, and even as they said in the original announcement, bosses can go up and down whenever the devs want. I do think we will see the gunship battle tested on the PTR at some point, though -- it seems like one of the more complicated encounters in the instance, and Blizzard will surely want to put it under a microscope sometime before the patch goes live.
Update: Apparently the gunship battle is live right now (4:40pm Pacific) on the test realm. If you want to see what it's like, get yourself a raid and head on in.