I also have the same problem with Lion 10.7.4. iPhoto will see the .rw2 files from my Lumix G3 but when asked to import I get the message 'Unreadable Files'. I have tried the recommendation that appears to work for some by copying the following command into Terminal :
/System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchSe rvices.framework/Versions/A/Support/Isregister –R /System/Library/CoreServices/CoreTypes.bundle/Contents/Library
but that didnt work for me. I got the message "No such file or directory"
Apple Help in UK had no idea and Panasonic UK say it's an Apple software problem !
Any help / solution would be greatly appreciated.