Ok, I'm going to answer this with a non biased post, no doubt people will go "AH YOUR JUST SAYING THAT COS YOU BUM STEVE JOBZZZ"
But here goes anyway...
I've had my Mac Pro for 2 and a half years now, I paid £1700 with the following spec
2 x 2.66ghz c2d XEON cpus
1GB of RAM (later added a further 8GB from Crucial for about £200 I think)
512mb X1900XTX ATI Radeon card
1 x 250gb Sata drive (added my own additional drives later
Bluetooth
Wifi
Now I was fully aware that I could've bought something which owned it spec wise for the money but quite simply I wanted to use OSX, its a lovely operating system which I much prefer over XP, Vista, or 7. So I would say part of the premium is the ability to use OSX.
The other part of the premium is the engineering and build quality put into these things is outstanding, I didn't realise it but when I first took the side panel off to add my hard drives the side panel has a rubber seal on the inner edge to outrule any addition noise, vibrations, or dust. I checked over the inside of the machine and realised in some sense it's a work of art, all the screw heads line up perfectly, so they weren't just rammed in and screwed down, but all done the same so when finished they all line up and look neat and tidy. There is not a single cable visible in the machine, despite the fact it has 4 or more antennas wired around the case for Wifi and Bluetooth. Each hard drive bay is numbered and even the screws in the caddy which everyone who buys one is bound to remove are all lined up as described above.
The RAM trays are on an easy access slide out mechanism so even the thickest of people can upgrade it.
The ONLY, and I really mean this, the only maintenance I ever have to do to it is once every few months is take the side panel off, remove the graphics card and blow it out with dust. That, is it.
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Next main reason why I bought one.....familys....
When I had a windows machine various people from my family would just hop on the net or use the PC when I was at work, which resulted in more often than not, coming home and having to sort the thing out with it being pop ups, adware, whatever. With the Mac it's left unlocked all day, everyday anyone can come on and use it and when I sit back down the most I have to do is maybe close a few windows they have left open.
And finally, which relates to the above, when you work in IT support and spend the whole day fixing annoying problems etc, last thing you want is to come home and use another windows machine, so it's nice to get away from it.