"Make sure you get the faster Xeons"5.0 starson by m4ch4x0r
Pros: Fast, easily upgradable, easy to work on, and dual I7 Xeon chips; up to 4 video cards if 3d performance isn't paramount. or you don't need additional PCI-E cards (fiber, RAID, secondary ethernet)
Cons: No standard blu-ray drive (you can buy one though), video cards should have two displayports instead of 1 displayport and 1 dvi port, wish it had a second x16 PCI-E slot and 2 more x4 PCI-E slots
Summary: First, to the whiners that complain about no blu-ray, would you rather pay $300 and easily install your own or give Apple $700? That's what I thought.
As for the machine itself, the slower processors (2.26 GHz) give mixed performance when compared to the last generation machines, but the high-end processors (2.93 GHz) dominate the previous generation 3.2 GHz machine in all but Photoshop (Adobe, when's multi-threaded Photoshop coming out?)
It also has a huge advantage of running much cooler than comparable machines, thanks to it's case design. The only part that even gets warm is the Radeon 4870 (if you get that option).
When paired with it's capability to run Windows, Linux, and other x86 or x64-based operating systems simultaneously with Mac OS X, this machine just looks better and better.
The only part that lacks, IMHO, is that Apple set the RAM limit at 32GB for the dual-socket machines and 8GB for the single-socket machines. Each processor currently supports 24GB of RAM (Intel design limitation), and even with neutering the single socket with 3 RAM slots, Apple should have went for 12GB and 48GB (respectively)
As for me, I've ordered mine with just the upgraded processors and ATI 4870 video card; 3rd party RAM is cheap, and the WD 2TB hard drives will be out real soon, which will lead to this being one heck of a HD video editing system and a halfway-decent gaming system as well.