You can now begin downloading the PTR (Public Test Realm) client for patch 3.0.2. We reported earlier today that character copies have been made active, and those are going along nicely as far as we can tell (my Warrior copied across with no problem). To download the client and copy your characters over to the PTR, login to your account administration at worldofwarcraft.com.
We are expecting a lot of out of this patch. From new talent trees, to class and raid mechanics changes, to the removal of the Amani War Bear. We'll have a lot more on this as we get more information in. Patch notes are not available yet – though we expect to get our hands on them soon.