I'm a long time PM user but only just discovered the Loupe Cursor. Trying it out on a contact sheet of images from various cameras. It works fine for Nikon NEF but no image is displayed for my Panasonic DMC-LX2 RAW files.
These images display fine in Preview.
PM 4.6.2 on OSX 10.5.8
MacPro 10MB
Memory Cache 1024MB