It appears that in my sleep-deprived state I've managed to change a setting somewhere. I'm pretty sure the Navigator used to display the effects of changes to print settings as I made them. It performs normally in the Library and Develop modules, but loses the image (goes to solid background color) when I go into the Print Module. It prints to paper or JPEG okay.
(Lightroom 4, Windows 7)
Okay, that makes sense, I just thought I remembered seeing images in the Preview. A senior moment.....
I also just managed to duplicate a problem I had last night. I printed several different images to file (JPEG), then for no apparent reason and without changing any settings, printing to file started creating images that were solid black (black is coincidentally set as the background color). After a little experimenting I found that printing in Draft Mode gave me a JPEG with the image, not solid black. The only option I had enabled in Print Job was Print Sharpening. Turning that off and then printing the same image to file again (not in Draft Mode) did give me an image. Then when I enabled Print Sharpening it didn't do it anymore. So now I'm back the the same settings, but I'm getting an image. Sounds like maybe something to report.