Yesterday, I had the chance to download and try out the new 64-bit client for WoW.
For a piece of "unsupported" software, it's rather nice.
Loading screens, particularly the initial loading screen, seems to complete much more quickly for me. Frame rates are generally better, to the point where I was able to do crank up my graphics settings to "Ultra" for the the Benedictus fight in Hour of Twilight.
Overall, very nice. I think I'll be using the 64-bit client for a while longer, maybe see how the frame rate performs in some more chaotic and crowded situations.
One note: the Mac link for "How to tell if you have a 64-bit operating system" are not quite correct. The link takes you to the Mac support page that tells you how to answer the question, "How do I tell if I'm using the 64-bit kernel?" Which isn't what you really want to know. You can run 64-bit applications on a 64-bit processor even if you're currently running the 32-bit kernel.
Instead, what you really want are the instructions that describe "How to tell if your Intel-based Mac has a 32-bit or 64-bit processor." My MacBook Pro is running the 32-bit kernel, but because it has a 64-bit processor, I had no problem running the WoW 64-bit client. I may follow the instructions on the 64-bit kernel page and reboot to use the 64-bit kernel, just to see if there's any additional improvements there; but the WoW 64-bit client runs just fine on my Intel Core 2 Duo system.