probably not what you wanted to hear... but time machine has been quite a nightmare for me on several occasions. I have a stack of time machine backup drives, set aside for the numerous times when time machine simply stopped working. Either automatic backups or ALL backups stopped working. Hours (approaching 20 in total I would wager) spent on the phone with Apple, trying all manner of resets, fruitless. "searching for backup..." or "preparing to backup" are where I usually get stuck. Sits there like that for days. No one at Apple can tell me why. Time Machine's logging is next to non-existant, there are NO useful logs to look at to see what it's major malfunction is when it's stuck trying to start a backup.
It's been my experience that if (when) time machine breaks, it breaks hard and all you can do is format the drive or shelve it and get another one. If you have a time machine that's not wanting to run backups for some reason, and manage to recover it without losing your backup history, count yourself lucky.
At the moment, my time machine is backing up normally. I really have no idea how long it will last. Owell, hard drives are cheap. I really don't mind that much at this point to just grab another one from my pile and make a new backup. I HAVE needed to go back to the stack a few times to pull out a file from a broken backup (they always are accessible, just can't be added to) so it's not really an inconvenience.
My mom's time machine backup went down in exactly the same manner and also required a nuke to get going again. This was not good though, as it had just stopped backing up a few months before they needed it. (iPhoto library somehow got trashed...) So there was minor data loss associated with the problem. Luckily I had an up-to-date offsite mirror backup running for her, and was able to upload it back (over the course of five days) before nuking the time machine drive and restarting TM.
She dodged a bullet - if she had not called me immediately in despiration the afternoon the library was deleted, it would have been gone for good, erased off the offsite backup that evening when it ran to update the mirror, and she would have had to settle for two months of lost photos.
Needless to say, I trust my rsync scripts a lot more than time machine, although its incremental backup handiness is difficult to argue against.
