A Google software developer and former Microsoft engineer wrote a blog post last year -- which I just stumbled upon while doing an unrelated web search -- about helping out his kids' nanny with a new PC.
She bought a new Windows machine and the salesman convinced her to pick up a Bluetooth wireless mouse along with it. She got home, clicked on the computer's Bluetooth button to synchronize it with the mouse ... and you can guess what didn't happen next. A week later, having RTFM'ed and made no progress, she calls him in. Even with a hardcore geek at her side, it takes several reboots, a number of ominous warning messages, multiple software downloads, and an afternoon of web research to figure out what's wrong with a Plug And Play device.
And I absolutely cannot spoil this story by telling you what the problem was. Read the whole thing, and the punchline will leave you stunned.
(Hint: It wasn't a user error.)