Today, the site was mentioned on badscience.net.
This evening, I noticed that the computer had dropped off the Internet, and that the air in the study smelt of that magic smoke that electronic components emit as they fail. I happened to have a spare power supply, and with this replaced, and the fuse in the power supply changed, the computer started working again.
The dead component was a Colorsit EN60950 Switching Power Supply; I think it's quite ancient, it may well have come out of a computer bought at the office in 2004 to be plugged into a case that I bought in 2007. Maybe five years is a reasonable innings for a power supply ... the last one that I had fail did so after six months.
To the pub now, I think, leaving for tomorrow the question of why compute node #2, which yesterday was happily transferring tens of gigabytes around by NFS, today denies having an ethernet interface.