As Adam pointed out earlier this afternoon, the changes for patch 2.4 are starting to be less and less dramatic, which may indicate that the patch is nearing completion. Here's another such indication: parts of the patch (251 MB for me) are now being sent out to the background downloader. This means that some of the patch data is finalized, and we can get those parts of the patch now instead of having to get everything on patch day.
Note that the patch is not, in fact, being released today, or even necessarily next week. But I would bet that it won't be more than a few weeks until the Sunwell is upon us. And when the patch does drop, someone's going to win fabulous prizes! More importantly, I'll have some new dailies to do. Hurry it up, Blizz (but don't release it before it's ready, of course).
Edit: Patch 2.3 was on the background downloader for 12 days before it was released, and 2.1 was 11 days. But 2.2 was on for over a month, so it's hard to predict for sure how this will go.
[Thanks, Amarius (and multiple other tipsters)]