My brother came to visit at the weekend, partly to take delivery of a brand new Mac mini I'd ordered for him. He's always been a Windows (and now *nix) user, but after a blown power supply on his old Windows machine, he decided that he wanted to get another small computer to run alongside it. All those years of steady but stealthy indoctrination from me must have had some effect, because he decided to get a Mac. If I'm honest, it probably had more to do with the fact that the mini is small, cheap, and he already had a monitor he could use with it.
When I held the handbag-sized box outstretched towards him with a flourish, the first thing he said (laughing) was, "Is that it?". I don't think that he'd realised quite how mini it would be. Anyway, we had a lot of fun setting it up, and I gave him a kind of whirlwind tour of Mac OS X, showing him the structure of the file system, the System Preferences and how to install applications.
I've used Macs for such a long time that many of its quirks and differences from Windows are invisible to me, so it was a very interesting experience to walk someone through the process. I think that he generally found it fairly intuitive, but certain things like clicking the close button and expecting the application to quit (which admittedly it sometimes does) might take a bit longer. At one point he asked me if the window widgets could be moved to the right hand sides of windows. "Err, no." I resisted the urge to say that the left hand side is the One True Location for window widgets, but it is funny how the system you use leads to such a strong feeling of the absolute correctness of one pattern or the other. I think that the different keyboard shortcuts will probably take even longer to adjust to, as I've found to my cost in the opposite direction when using Unix applications.