After using this 2006-2007 model 2.66 Quad-Core Mac Pro with the 23" Apple Cinema Display for several months, I remain very impressed.
The Mac Pro came with Tiger OS, a smaller Hard Drive, only 1gb RAM in dual-channel mode and a weak Video Card to keep the cost as low as it was. Upgrading to 8gb in Quad-Channel mode made a huge improvement in video rendering performance, followed by more and larger hard drives in RAID, a better Video Card and installing Leopard OS. This is by far the best, fastest and most stable computer I've ever used. It is virtually silent and utterly reliable. It "Renders" video footage far faster than any PC I've ever used with fewer errors or crashes. I can't recall Leopard itself EVER crashing, just an occasional Application. Another bonus: Apple's Operating Systems (Tiger, Leopard) cost a LOT less than Microsoft Windows and DO NOT REQUIRE "ACTIVATION" (which was driving me bonkers with my High-End PC).
The outer casing is a work of art with phenomenal fit and finish. Common upgrades such as Hard Drives, Optical Drives, Video Cards and Memory Modules are all straightforward. The interior is free of loose wiring and clutter. Everything inside and out is well thought out and executed. I cannot think of any better way to build a computer.
As awesome as this "Last Year's Model" is, I wonder what the new EIGHT CORE Mac Pro is like. I'm sure that (or it's successor) will be my next system.