Update: Finally available!
As I usually use the PNM format as a very minimal container for image data to dump for debugging in low-level places (e.g. even drivers as it only requires a few lines of code) I missed the ability in Apple’s Mac OS X to display PNM files (apparently even the Photoshop CS2 does not support it!).
As I spend rather much time on some OS X code these days, I stuffed together a Quick Look generator plugin for any UTI (file type) supported by our ExactImage.
If you are looking for such a plugin let me know - I’ll also probably publish it later when I find some more time.