For Adobe Photoshop pros, the new dual-2GHz G5 is a dream machine. After you work on one for a couple of hours, it becomes very clear that the machine changes all Photoshop's traditional pain points. This makes many old workarounds unnecessary, but it will probably require new ones as we learn where the new bottlenecks are.
Right from the start, this machine feels fast while running Photoshop. Menus don't so much drop down as fly in your face, and you may need to slow down mouse tracking, at least until you get used to the speed. However, while the new machine does wonders for Photoshop, don't expect miracles.
The biggest bottleneck in Photoshop has long been getting data from RAM (or worse, from the scratch disk) to the CPUs. The memory bandwidth in the G5 is about an order of magnitude wider than in any previous hardware generation, which makes a huge difference in features such as the Healing Brush, or in redraws of layered files with complex blending. But until Panther has been out long enough for Adobe to perform rigorous tests, Photoshop will still be limited to using 2GB of RAM.
Once you exceed that limit, you're back to having Photoshop read the scratch disk, and while Photoshop's caching of the scratch volume is very sophisticated, you'll still see significant slowdowns. (Even though the dual-2GHz machine I tested had 4GB of RAM, it wouldn't let me dedicate a full 2GB to Photoshop -- if you're considering maxing out your RAM for Photoshop use, 4.5GB seems like a good amount for now.)
Reading from and writing to disks is quite speedy using the stock 250GB serial ATA drive, but serious Photoshop users will almost certainly want something faster. Finding out just what that something should be will require more research, as drive vendors won't quite say whether it will be possible to attach an Ultra SCSI RAID 0 array, or even a FireWire 800 RAID 0 array. We look forward to numerous online debates about the relative merits of each, but even a second serial ATA drive with a dedicated Photoshop scratch partition would undoubtedly lessen some of the pain.
Any way you look at it, the dual-2GHz G5 is an extremely fast machine that will delight Photoshop geeks. But it's more than a little scary to contemplate just what the Photoshop engineers will do with all that power in the future. Meanwhile, having ordered my dual-2GHz G5 approximately 16 hours after Apple started taking orders, I want it now!