Google earth (the mac version) has now started to insist that the latest version is a "mandatory upgrade" and won't let me run the old version. The new version won't run on mac OS-X 10.3.9, it needs 10.4... And I'm really not going to pay a hundred pounds or more for an operating system I don't otherwise need. I'll try complaining on the forums again, but I suspect it won't do much good.
Later: On checking the Mac forums for Google Earth it looks like this is a bug with the automatic update program which Google are trying to fix.
VERY later: Turns out that shutting down the Mac and restarting appears to fix this. So far, anyway.