Right, I had to register to post here so I'll get my piece nice and clear. I can tell you a few good reasons to, and not to, buy a mac. My experience is with a Macbook Pro, so I'll restrict it to laptops.
For;
Portability. Macbooks have excellent battery life-- even the base models have 10 hours now. They're also sleek-bodied with few catches, and with a keyboard skin susprisingly spill/accidental immersion proof (I've killed a couple HP Pros, my second preference, this way.) I could not find another laptop that satisfied my "10 hours battery life, full power CPU" requirement, whatsoever. None. Have a look yourself and see what you think.
OS usability; They're probably the easiest to jump into; they don't ask you to make any decisions that have the ominous "I might kill this" feeling that a lot of newbies face. The OS has built in spellchecking absolutely everywhere (right now it's checking for me here, for instance), and a lot of the applications integrate with ease.
Quality: People can say this is subjective if they like, but I've had two HPs, Dells, IBMs, a couple Toshibas and an NEC from Japan, and the nicest machine I've had to use is this Macbook. The screen has a layer of glass over it so you can actually clean it, and the touchpad is huge, expressive and coated in glass for minimal drag. The keyboard's well spaced, and backlit, for goodness sakes, and the laptop doesn't have extraneous panels or catches or lugs, or even non-flush screwmounts. Oh, and see if you break the power cable on a Macbook. Or drag it onto the floor accidentally. Betcha won't!
The end-user experience; You get all the fruit with a basic Macbook (even a graphics card with dedicated memory, despite what someone else posted), and they'll pretty much do anything they're asked. They're looked after well by Apple, too; Warranty issues are little drama. Also you don't really need anything but Office to start using it right away-- you get all the basics from recording software to photo organisation to a calendar that's worth a damn, and don't need to download a thing.
Against;
Unfamiliarity. If your dad's "computer literate", but not a proper user, moving over to a Mac is going to be an awfully confusing experience. The tutorials ease the pain a little bit but trying to figure out some of the basics of things like installing software can be a pain if you're not used to it.
Cost. Agreed, power for power, a Mac isn't fantastic value. I wouldn't ever buy a Mac desktop, and the only reason I have my Macbook is the sheer fact I couldn't find a PC that matched my required specs, and wasn't a custom order (I hate ordering custom machines; Compromise makes me unhappy). You do get outstanding features and outstanding battery life, but at outstanding cost; Your choice.
Integration issues. Try and share a printer in Windows 7, then allow your Mac to use it. There's forums full of posts like "On hold; Authentication error", and Apple has remarkable levels of oversight when it comes to allowing their precious machines to integrate into a network.
Software, software, software! Try finding a NISSAN FAST reader, or any other specialist tool, for Mac! They're just not there, and if you have to run VirtualBox all day or boot into another OS, you're missing out on some of the benefits of a Mac in the first place. They do miss out on an awful lot of specialist tools. It's that simple.
At the end of the day, there's no reason to be afraid of a Mac. It's beautifully made, expensive x86 hardware, that runs proprietary operating systems. That's all there is to it. You can even run them pure Windows if you like-- a good friend of mine wanted one he could do output specs on dynos with, all day, without recharging, and his Macbook (Unibody, non pro) doesn't have OSX accessible anymore. It powers on straight to windows. No, I don't know how.
But really. Mac's really quite nice, whether you're running 7 or OSX, but you really, really, really do pay for it. Six of one, half a dozen of the other. Now you're armed with more info at least, not just bullshit "MACS ARE FOR GAY MEN WITH HERPES" crap.
PS; Also, the right click stuff? Bullshit. I have right click via tapping or clicking the bottom right corner, things I never found on a windows laptop. Just a note to the person up there who never seems to have touched a Mac recently. This is the first touchpad that has made me not want to bother carrying an external mouse; The external mouse can't do as much as the touchpad!
-- Numbers
(PS; Sorry for the edit, forgot a bit)