According to Eyonix, the background downloader for patch 3.3 will begin its work soon. There were some reports that it was turned on yesterday for a short time, when it began to deliver a roughly 450mb pre-patch file. However this time, Blizzard is turning it on for good.
Eyonix points out that the background downloader should provide a faster download than normal. Go into the preferences of the downloader and check "Don't throttle background download" to see the new speed in action. However, this option has often been known to interfere with WoW and other applications accessing the intertubes, so I recommend you only turn it on when you're not going to be doing a lot of online activity.
This does point to patch 3.3 coming soon. Whether or not that soon is next week is too early to tell, but usually Blizzard runs the background downloader for a couple of weeks before rolling out a patch. But who knows -- we haven't heard anything yet on (or off) the record.
Update: Many readers are reporting that the downloader is now active.
Patch 3.3 is the last major patch of Wrath of the Lich King. With the new Icecrown Citadel 5-man dungeons and 10/25-man raid arriving soon, patch 3.3 will deal the final blow to Arthas. WoW.com's Guide to Patch 3.3 will keep you updated with all the latest patch news.