A couple of further observations about 10.5.2 and the way it handles GX100 RAW .dng files:
The .dngs really are handled as just another graphics file by the OS. Not only will Preview and iPhoto dislpay them, but the OS makes a graphic icon for any .dng viewed in the Finder. Furthermore, the media inspectors see and handle the files, and so they can be dragged into Pages documents, TextEdit documents, etc. If you paste a GX100 raw file into a TextEdit document, it's automatically sized for the document and displays just as if it were a jpeg. But if you save the document and open its package (.rtfd files are saved as OS X packages) you will see that there is no jpeg but only the original, full sized .dng. I'm not sure what good this does, but it's certainly cool.
This new feature of OS X should mean that any camera, now or in the future, that uses .dng as its RAW format will automatically work with all Apple programs.
Also, any new camera that _doesn't_ use .dngs and isn't yet supported by OS X may be usable if there is a RAW to DNG converter for it (such as the free, standalone Adobe converter).