Good news: I finally got my iBook back from Apple, repaired with a new logic board.
Bad news: they replaced the 900 MHz board with a slower 800 MHz one.
Needless to say, after two and a half weeks’ wait, I’m very dissatisfied to have my computer downgraded. I phoned Apple. No apology; they insist that they must contact the repair centre first to check that it was really 900 MHz. Translation: they don’t believe me. This is despite the fact that it was a built-to-order machine, and that I have the original warranty card stating its specification—and Apple must surely have the same information as well.
It will apparently take them several days to get an answer from the repair centre—the very people who have already proven themselves unable to identify processor speed correctly. I’m not hopeful.