I read about 4 pages then I got so wound up I decided to skip the last two and go ahead and write something.
As an owner of a Octo core Mac Pro I can say from experience that the most powerful Mac does not fulfill all my needs. As a result I have a PC I use for gaming which I consider to be ridiculous given I have just bought a £xk Mac.
The argument that Macs do not appeal to "gamers" is entirely flawed. I would much rather be able to boot into Windows on my Mac Pro with multiple GPUs in SLi or Crossfire than have to constantly switch between using my Mac and this disgusting piece of hardware Alienware calls their ALX tower.
The argument that Macs aren't built for gaming is also completely preposterous. If Apple wants to continue to expand in the future its going to have to go more mainstream with its products and Apple has shown interest in doing this by introducing boot camp and Safari on Windows.
The problem is not that the Mac Pro is too expensive but that it is unsuitable for prosumer use. Contrary to the belief of many users on this forum, the prosumer market is growing faster than any other with the general populace becoming more and more tech-savvy. The Mac Pro's RAM, multicore CPUs and GPUs are unsuitable for gaming and general home use all together. The enclosure is much to big and games still don't make use of multiple CPUs. Adding additional graphics cards to your Mac Pro won't make a difference as they can only be used to power additional monitors and can't be used together in crossfire or SLi. The FB-DIMMS aren't at all suited for low latency gaming and altogether the performance of the Mac Pro in gaming scenarios can't justify the price.
Up to date GPUs aren't even available for the Mac Pro yet with the 7300GT as standard and the past-generation X1900 as your best option to upgrade to.
This prosumer desktop (which I doubt will ever exist) should consist of the following components.
Enclosure 3/4 the size of Mac Pro chassis.
Intel C2D Conroe/Penryn
2GB DDR2 SDRAM at 1066MHz
SLi support for latest Nvidia cards or Crossfire for ATi
People often tend to use the excuse that "500GB is far too much for most users" or that "nobody needs a 3GHz processor". Well maybe people don't need an excess of power however when the competition is priced likewise you want an advantage over your opposition in terms of technical specifications. Bigger = better.
PS. Just to demonstrate how disgusting the ALX is, have a look at the size by side comparison featured on Alienware's website:
Feel lucky that you've got a Mac.