Apple updated the built to order parts on the Mac Pro. You can get upgrade the quad-core Mac Pro from 2.93Ghz to 3.33Ghz for a whopping $800. This option isn't yet available on the 8-core Mac Pro. Besides this Apple also updated its available drives. You can now get a 2TB drive for the low low price of $500. Or you could upgrade them yourself and be done for $200 per drive.

I personally wonder why you would want to get a Mac Pro though. The new Core i7 iMac is cheaper compared to the Mac Pro and it includes a 27" screen. The speed difference is near insignificant. The biggest difference is probably that you get to upgrade system parts with ease. But if I was a professional I'm quite sure what I would choose, and it ain't the big box with holes in the front.