Thank you guys. Well, indeed I had to reflash. But, happily, that brought back my phone to a working state. I enabled extras testing, installed BackupMenu, rebooted, and restored my backup. It went well. I've lost the history of a few conversations, probably a few recent Contacts, but no big deal. I'm back in business, loving my N900.

Good thinking - CSSU updates touches many files, that otherwise "sleep" undisturbed by write access. It's more likely to get filesystem corruption manifest itself after CSSU update/first install, than any particular single package, I think.

/Estel