Yesterday, after a mammoth session importing and organizing photos in Aperture 2, Time Machine informed me that the backup drive was full.
That didn't bother me—it was inevitable—but what did disturb me was the rest of the message. It told me that the earliest backup was now February 18th. In other words, it had eliminated everything from November 19th thru February 17th.
I knew what the behaviour would be when the disk filled up but I didn't expect it to eliminate so much in one go.
I suspect that I would be more likely to want to find stuff from November to February than in the last week although maybe I'm thinking of Time Machine too much as version control rather than backup. Still, I would have preferred it to sacrifice more recent backups rather than eliminate the oldest stuff.
There is an option "Warn when old backups are deleted" in System Preferences which was checked but I'm not sure if that means "tell me when old backups have been deleted" or "tell me when old backups are about to be deleted". My recollection of the message yesterday was that it had already done the deed and there wasn't anything I could have done about it.
Either way, I wish the behaviour in this scenario had been different.