If you've received such a paper-lashing (and have recovered from the shame of same) you know that, even with the best intentions, we sometimes leave these jobs undone. So that I may avoid a week on the couch, let me offer some general pre- and post-upgrade advice for those working on a loved one's computer.
If your victim is like most people, they will have entered an e-mail password once and then promptly forgotten it. Before performing a major upgrade, ask them if they know their e-mail password(s). If not, ask for their administrator's password and have a look around the Mac's keychain, making note of the e-mail passwords you find.
Also, travel to ~/Library/Keychains, make a copy of the login.keychain file, and tuck it away in a safe place (on a USB key drive, for instance). Should you need to rummage around in it later because some password didn't survive the upgrade, you can move some of its passwords or other login information to the new login keychain. (I'd do this by renaming the old keychain file, opening it in Keychain Access, and dragging the needed items from the old to new keychain. You'll need the Administrator's password from the old account to do this.)
You know what they say about assuming. Yes, I assumed that the printer would work after the upgrade but didn't bother to test it. Turns out that Leopard didn't include the printer driver for my wife's HP LaserJet printer. Had I tried to print I would have known the printer was MIA and would have taken steps to download the driver directly from .
Go ahead and sever your connection to the Web for a day and see how you like it. Thankfully this is something I did. You should too.
People spend a lot of time with their web browsers and as the person responsible for making someone comfy with their new computing environment, part of your job is to ensure they have a similar experience with that web browser after the upgrade. My wife had never seen Safari 4's Wall-o'-Sites and didn't care for it. (Fact is, neither do I.) For this reason, pay attention to how the browser once looked and try to duplicate that look after the upgrade.
In my case that required opening Safari's preferences, clicking the General tab, and choosing Empty Page from both the New Windows Open With and New Tabs Open With pop-up menus and leaving the Home Page field blank.
A good auto mechanic test drives a car before returning it to the owner. And during that test drive, the mechanic steps on the brakes at least once to make sure the car stops properly.
The example for us upgraders is that while the Mac may seem like poetry in motion when it's operating, it's essential that we go all the way--start it up, use it, and then . Seems that the HP printer installer on my wife's iMac left some cruft running that wasn't visible from the Dock. And that cruft was enough to prevent the Mac shutting down. I was able to launch Activity Monitor and kill it, but this isn't something she would have known how to do.
Have humbling upgrade tales of your own? (You know you do.) Share them with us in the warm and supportive environment we call the Macworld Forums.