For those who are jumping up from a 2006-2007 to a 2008 or 09 mac pro, based on what I have read and researched the higher end 3.0 and 3.2 2008 mac pros offer a really good advantage.
The 8-core 2.8, while being the lowest of the 2008 family is slowly fading out though its architecture is mainly the same as the 3.0 and 3.2. Many have suggested on here that if one uses SSD drives in a RAID then you will have a nice fast system in terms of storage. When asked if it would be worth it to go from a 2008 to a 2009 the answer for 90 percent has been mainly no real gain except for a few minutes in rendering. But, for those who bought the 2008 mac pro for everyday tasks like I do + bootcamp, it makes a very fast and fine machine.
Just the very notion that the 2008's have EFI64 means there certainly exists the upgrade path for "future" video card options, one of which I can't wait: The Radeon 5870 and the other family of 5800 video cards. Will Apple market the 5870 for the 2010? This is anyone's guess, but at least those with 08 mac pros will be able to continue to upgrade to faster and more powerful GPUS due to EFI64 that is until EFI128 comes out.
As Nano pointed out in many posts awhile back, the Mac Pro's days are possibly going to be numbered as Apple is shifting away from the pro market , mac pro, and xserve and replacing all that with the electronics such as: Ipod, Ipad, Iphone 3gs, and other future mobile devices.
Apple is going to thrive where they will make the most money, and sad to say it isn't the mac pro, but rather the above mentioned devices.
But in reality, by the time the EFI128 standard comes out I am sure the Mac Pro and Xserve will most likly fade away into history and be replaced by its possible successor: The Imac. Again, this is all pure speculation, but the way things are going - Intel is running out of options for XEONS and the Gulftown family appears to be the LAST of the XEONS. The only way the Mac Pro might have a future is if it moved to consumer based core ix series processors and used desktop non-ecc memory.
Really who needs server grade memory these days unless one is using a machine as a server and not a workstation.