I'm sure there will also be minor changes to functionality in Outland and Northrend but not much in the way of geography changes in these zones. Ditto the zones that came with Burning Crusade's new races, which includes Silvermoon, Eversong Woods, and Ghostlands, plus the Exodar and its associated Isles.
Some time (a few weeks?) after the patch is rolled out, the Cataclysm expansion will be released. This will contain new races (Goblins and Worgren) along with their starting zones and new high-level zones to get your characters from level 80 to 85.
This distinction between Cataclysm the expansion and Cataclysm the patch really sunk in for me when I realized that there are two completely different test programs currently under way, each with their own servers: the PTR (public test realms) and the Cataclysm beta realms.
I believe the PTR realms are open to anyone, regardless of whether you've been invited into the beta, so if you want to see what the newly revised Old World zones will be like, head over to your Blizzard account and see if the PTR realms are available to you.
Be prepared for a giant download, though! The Cata beta is over 22 GB on my machine, and I suspect the PTR client is about the same size.
If I understand the process correctly, many of the changes I'm encountering in the beta will be delivered with patch 4.0, which will be arriving sometime in the upcoming weeks, prior to the release of the Cataclysm expansion. As of October 1, my computer has already downloaded about 4 GB of the patch. I'm sure there will be more.
By default, patches are downloaded automatically after you exit WoW. You might want to check your computer to see if you've gotten these updates yet. If not, you might want to leave your machine running overnight to let it download them.
Here are the default locations:
Mac: Macintosh HD/Applications/World of Warcraft/Updates
XP: C:\Program Files\World of Warcraft\Updates
Windows 7 and Vista: C:\Users\Public\Games\World of Warcraft\Updates
The files I have on my XP PC are named:
Yours will probably be named something similar.
BTW, by default the downloader uses a BitTorrent protocol, which is great if your router is happy with having zillions of connections constantly opening and closing. Mine isn't, and I found the download to be much faster when I disabled Peer-to-Peer Transfer in Options->Downloader Preferences in the WoW launcher.
Getting into the Beta
If you are interested in getting into the beta, here is a video on how to do it:
A lot of new people seem to be coming into the beta now; I think Blizzard is expanding the population to get more testing done before the release. If you are playing regularly may increase your chances of getting in. And if you pre-order a copy, I'm sure that wouldn't hurt your chances! My invite came a few days after I made my pre-order.
Speaking of release dates, the latest rumor is that Cata will be out in January 2011. Apparently Amazon sent out an email to its preorder customers saying that it will be delivered in January. So there should be more time to adjust to the upcoming patch 4.0 changes before Cataclysm itself hits.