Note to self: The patch is big.
My background downloader had taken care of the 4+ GB over the past few weeks, but I was surprised that after that installation, another window started up for first a 50MB and then another 1.4 GB download. I've no idea if there's a fourth download behind this one, but hold onto your hats.
EtA: No, there wasn't another gig lurking behind that fifth one, so we're good to go. The "you can play now" sound pinged halfway through the last 1.4 GB download, but since the servers were down, it was a moot point.
All in all, lots of "Deathwing this" and "Deathwing that" files were unpacked along with the plethora of assorted other data.