My committment to my assertions in my August 8 entry is wavering slightly in that the 3GHz model of the Apple MacPro has proved to be very fast indeed at some Adobe Photoshop CS2 tasks, and is faster on Adobe After Effects, even though both are emulated.
However, I stick to my original advice that buying a MacPro now is too early if you also need lots of memory—it’s just too expensive as of yet.
I paid about $800 for 8GB of ECC RAM for my PowerMac G5 Quad (non-Apple, 3rd-party). Compare that to about $2500 (from Apple) or perhaps $2000 (3rd-party). If price is not a significant consideration, the MacPro looks like an awesome machine, even for Photoshop users. But verify performance with the specific features you use before committing.
Of course, if you are buying new, my advice remains to go with the MacPro—any extra money you spend on MacPro ECC memory will be no worse than the depreciation on a PowerMac G5 Quad.
Please see barefeats.com for SHOOTOUT: Quad Xeon 3.0GHz Mac Pro versus Quad G5 2.5GHz Power Mac on the MacPro 3GHz and Photoshop benchmarks.