Been waiting for this: Adobe Brings Photoshop Lightroom 4 to Mac App Store (app store link). Of course, you lose the cross-platform ability (I think), though if the software needs a license key, that should work for a windows machine as well (permitted by the license I believe).
Speaking of adobe, Continuing a proud tradition of user hostility is the story of installing CS6.
Update: The Brooks Review confirms that you only are licensed for Mac, not dual. Something to think about.