I attempted the Mavericks upgrade on my old (2009) Mac mini, which is several versions behind (10.6.8).
After the lengthy download (with no progress bar in the old version of the Mac App Store), the computer rebooted and attempted the install. A few minutes into it, I encountered the following error message:
The OS X upgrade couldn’t be started because the disk Macintosh HD is damaged and can’t be repaired. After your computer restarts, back up your data, erase your disk, and try installing again.
Click Restart to restart your computer and try installing again.
Clicking “Restart” leads to a restart loop, as on rebooting it reattempts the Mavericks install, resulting in the same error message. Apple’s online support was unable to fix the issue (and recommended Recovery Mode, which of course didn’t work, as this feature was introduced after 10.6.8.).
So, the long and short is, my computer is now unusable, thanks to attempting the Mavericks upgrade.
Thank goodness I have a backup. I hope it’s usable.
(The install on my much newer MacBook Pro took some time, but went without a hitch.)
UPDATE: After a trip to the Apple Store, the tech wiped the disk and installed Mavericks. In the end, I had to hang around the mall for a couple of hours during the install, and restore from backup when I returned home. All together, it ended up taking most of the day.