While I was away today I decided to have my workstation rebuild itself "from first principles" as it were. That is, to use the "emptytree" flag to rebuild the whole software stack from scratch. It managed to get through 227 of the 400+ packages involved before it encountered something it couldn't build. There are 5 or 6 major packages that the system currently can't build (KDE being the most annoying; I'm telling the system to try building that now that the major sub-strata have been rebuilt).

Would be nice if the emptytree option had a "skip anything that fails to build and report on it at the end" sub-option. Oh well.