For less than the price of your self built machine, I bought a HP xw6600 workstation with Xeon QC CPU and 10Gb ECC RAM - refurbished, but you can't tell the difference and I've had no problems for 6 months. And this is a very nicely designed workstation with fair amount of upgrade potential.
You can't do that sort of thing with the Apples. Need to do SLI on two PC compatible nVidia cards - you are out of luck with the Mac Pro - you can only buy compatible cards Apple sells for a premium. Want to use particular hardware and OSX offers no drivers for it? Out of luck. (No - third party drivers are either unreliable or simply non-existent for OSX in most cases. And then Apple keeps breaking things. Say what you will about Microsoft but they have improved the driver situation - even for Vista x64 - quite a lot - plug in any damn thing and it will get the right driver automagically.)
On the other hand, I like Mac Laptops. I have 2 MacBook Pros but both of them needed $349 Apple Care - they had to replace the logic board twice and top case once. But I stick with them as a matter of liking.
So yes, I think Apple is overpriced, offers the least options/compatibility and the quality/reliability isn't drastically better than the PC counterparts. Thus it just becomes a matter of liking and ability to spend the extra bucks which determines if a person is going with a Mac or PC.