It works ... even with peripherals !
"All those people convincing their friends and relatives move to macs, do you consider the problems when they want to buy a new printer? An external drive? A webcam?"
Ah. That would be FUD. Unintentional, maybe, but FUD nontheless.
If there's a printer that doesn't work with OS-X, honestly, it's at the arse end of the market, or there's one next to it in PCWorld/Comet/Wherever that works.
I have 2 Lacie drives (USB/FW400/FW800), 1 Maxtor (FW400/USB), 3 Western digital(USB). I've had 2 cheap enclosures (one firewire, 3.5" drives, one USB 2.5"). I never even considered that these might not work, and didn't get a nasty surprise.
Not ALL peripherals will work, granted, but it's simply not a problem to find something that does. Generally (but not always), installation is simple. The instructions for my bluetooth dongle, for example, ran to 12 pages for XP. For OS-X, it pretty much just said, "err, plug it in".
I've never had to install a driver for a camera. The drivers for my printers were installed automatically.
The majority (excepting the mini and the pro) of macs come with a webcam built-in, so when picking a machine, this should be considered. If they got a mini and then wanted to add a webcam, these people who I've selfishly plonked onto the Mac (to reduce my unpaid support calls), well they're going to call me and say "I want to get a webcam thingy. Can you get me one ?", and I'll say "Yes", spend 10 minutes looking for something suitable, and find a few user reviews to say they're OK, and then just get it.
The one you missed was software of course, but I don't simply say "Oh. You should get a Mac", I ask what they want first. The chances are that if they're asking me advice, they don't need Autocad. If they want it to train for cycling, and they cycle computer only does XP (this was true about 3 years ago, not sure about now), then I wouldn't necessarily recomnmend a Mac. If they wanted to gather live match stats in order to take their side to a Grand Slam, I'd have to recommend a Mac.
So it's not black and white. Specialist use needs particular care. For geneeral use, really, any drawbacks in software choice is usually made up for in software quality (less shit); other drawbacks (iPlayer oly streams to a browser), is a small price to pay for the _current_ position vis security. There's no need to run anti-virus software etc at the moment (but we know we probably will have to at some point).
And no, they're not perfect by any stretch of the imagination. My anectodal experience tells me that I get a lot less hassle supporting a Mac than a PC.