I am curious about this as well. I have been on the fence for months at my company as to when and how to upgrade our PowerMac G5s. We have Adobe CS5 shelfed, just waiting for an Intel processor...I have it at home on my iMac and CAN'T WAIT to unbox it here at work.
I've been going back and forth between an 8-core or quad core for my machine. I will be doing work in Premiere, After Effects, Photoshop, InDesign, Dreamweaver and Illustrator, with some DVD authoring and music on the side. I know CS5 has some potential for all 8 cores, but I do not know if the extra $$$ is worth it in terms of speed. One day I think 2.26 8-core, 12 GB RAM. Then the next, 2.93/3.33 quad with 6GB/8GB RAM...oh, just wait one more week for upgrades.... I usually like to run with several Adobe CS3 apps, mail, three browsers, Excel, Word, and Navicat open at the same time, and this machine is fast enough for daily work, but it feels and performs slower even than my iMac at home.
The other machine I will be purchasing will not be used for any rendering or motion graphics, so I am not as concerned about it (base quad, base RAM, 512MB ATI). But mine needs to be a beast in comparison.
Will Adobe CS5 apps make the 8-core model worth it? Any one have any real experience or knowledge of the two compared using the CS5 apps?