So, I'm having an unusual problem with both the combo installer and the MAS installer. The update downloads and launches without issue, and takes me to the "Restart" button to begin the update. After clicking Restart, the screen goes black, and the cursor disappears, then reappears a few seconds later and sits there on the black screen. The computer stays this way for a LONG time. I've left it for about an hour with each of the two updates before giving up and powering down the machine. During this time, the mouse remains active (cursor can be moved around) and the hard drive indicator is flashing busily. I've heard some indicate a long period of "black screen" on Restart, but mine seems unusually so. Is anyone else having the same problem, or any creative suggestions?
I will be trying again and leaving the machine to try to do its thing overnight, when I can leave it for hours straight uninterrupted. Thanks, everyone, for your contributions here!