If you’re impatient and don’t want to wait for the Background Downloader, you can download the patch from a mirror here:
You want a patch from the US column in the first table.
If you like to use BitTorrent with your favorite client (I like uTorrent), grab the official torrent file from the last row of the first table (the one that has “worldofwarcraft.com” next to it). This uses the same torrent that the BackgroundDownloader uses. Here’s a direct link to the torrent:
For full patch notes, go here:
There a link to undocumented changes on that page, but the list is currently only one item. I expect that to grow as people discover changes not in the official notes.
(Should Eldre’Thalas be down for patch fixes, remember to check our Horde guild <Geriatric Ward> on Aerie Peak.)