The Ubuntu people seem to have recently pushed to users a new version of the CUPS printer scheduler that doesn't like the syntax of some old cupsd.conf files. This breaks all printing on affected machines.
So where are the bug reports? Stack Exchange. Nobody over there is going to fix it. This needs to be discussed on Ubuntu Forums, where the maintainers might read it. For now, I posted similar discussions on the CUPS forum and Ubuntu's own forum, and linked them to each other. There's a finger-pointing problem coming up - is this a CUPS bug or a Ubuntu bug? (What writes the cupsd.conf file anyway? Ubuntu Settings?) I don't want to file a bug report until the finger-pointing phase has commentary from people who actually know the innards of Linux printing, or I'll get shot down by one side blaming the other. Let those guys fight it out.