For those of you wondering about Lightroom compatibility with Leopard, the answer is in Adobe’s Support for Mac OS X Leopard PDF. In this document, they state Lightroom 1.2 is not fully certified for Mac OS X Leopard and that future updates will address areas of Leopard compatibility.
From reading the Adobe Photoshop Lightroom User to User Forums, there are quite a few problems. More than I would have expected. In particular, printing seems to be busted. Hopefully, the update to address areas of incompatibility will be in the not too distant future.