I can't find the original post by Robin (Robster50), only all the references to it, but here are the instructions, again. I don't know how I missed them earlier:
Instructions
1. Pull out your ethernet cable and disable WiFi and any other network connectivity you have.
2. Open Finder, go to your computer and then select you Macintosh HD (or whatever you have renamed it).
3. Go to Macintosh HD - Library - Preferences
4. Scroll all the way to the bottom of the list and you ewill see a folder called SystemConfiguration
5. Pull this folder onto the desktop.
6. Go to System Preferences - Sharing and change the name of your computer, even just a litlle bit.
7. Reboot
8. Re-enable Wifi and Ethernet
9. If you have installed Jettison, remove it and remove it from your start up items.
Thank you, Robin. i did this last night, and after almost 24 hours of using the computer and/or having it in sleep mode, no disk ejections at all!
After I rebooted, the SystemConfiguration folder appeared unchanged from before, so I saved it on an external drive and deleted it again. Then I rebooted again, and the MacBook Pro booted up as if i were a new user entirely--clean desktop, new user icon, etc. So I manually replaced the SystemConfiguration folder I had saved, changed the name of the computer again, slightly, rebooted, and all was back to normal, but with a completely new SystenConfiguration folder containing only a few items. I had to go into system preferences to re-set up power preferences, etc., but otherwise the system was, and is, working perfectly, and maybe the problem is permanently solved.
I wonder whether simply removing some of the old plist files from that folder--the ones left over from the previous upgrades of computer and OS--would also do the trick. I'm thinking especially of the power management plist file that was in that folder, and which in my case was very old. We'll never know.
In any event, if this is the solution for most people, Apple should have it very visible and available to all AppleCare support people, and maybe Apple should even include a script for these actions to be used when people upgrade computers.
Ken