Shortly after installing Mac OS X Panther 10.3 (retail boxed copy), I discovered that I could no longer print to my Xerox laser printer (AppleTalk over ethernet). On each occasion the print monitor window would show the file apparently being processed (sometimes I'd glimpse a message: "Empty print file!") but it appeared that no data got as far as the printer. Deleting and recreating the printer made no difference.
After a restart the problem cured itself.
I hope this will save someone a lengthy trawl through plists and other configuration files.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20031021130350897