Or should I have said "Look out for Outlook"?
John from IT Support called with a couple of good ideas about my archive failures, so I followed his suggestions and ran a repair tool over my archive.pst file - it reported around 500 errors, then claimed it had fixed them. That did no better, though, so we figured that folder permissions within the PST file were screwed up as a result of my reinstall; I then renamed the existing archive.pst and restarted Outlook, which complained a few times (more than I'd want to wish on your average amateur) then eventually archived to a new pst. So we're sort of OK, I suppose.
I don't expect this has impacted Microsoft's bottom line, though.