Bare Feats has a new performance analyzes of the new Mac Pro machine, this time using the 3GHz model. When compared against a quad-G5, the Mac Pro did fairly well on the Photoshop CS/2 tests - the Mac Pro is 5% slower on the Photoshop test but 8% faster on the After Effects test - both running under Rosetta emulation. The Mac Pro 3.0GHz was as much as 85% faster when running native "universal" applications.
Keep in mind that you can always dual-boot a Mac Pro into Windows and run Photoshop natively (try to do the reverse on a Dell and see how far you will get).
A Windows user contemplating the switch to OS/X, the Mac Pro becomes a very easy decision - a killer machine, competitively priced, with two supper fast 3GHz dual-core Xeon Intel chips, and the ability to run natively OS/X and Windows applications. If you have already invested a lot of money on Windows applications, and Windows itself, you can continue to use them on your new Mac Pro as you slowly migrate your work-flow to Mac OS/X.