According to the official Lightroom team blog, we’ve got a few weeks to wait before we’ll be able to run Lightroom seamlessly on Leopard:
The good news is that we’ll be releasing an update in mid-November that will address key compatibility issues.
OK, I know this takes time, but arrrgh. But wait, there’s more!
The interaction between Leopard’s Time Machine and Lightroom’s catalog files is unknown at this time. Running Time Machine backup or restore operations while Lightroom is in use is not recommended until more information can be obtained.
So, even if you’re willing to put up with not being able to print and import dialogs disappearing under the main window, be careful out there.