I think of it this way. Do you want to invest money in older technology, or new technology.
ALso, all product updates in the future will be intel and not powerPC so sooner rather than later the G5 will have less use when compared to the macPro
Mac Mini i7 (mid-2011)
Arguably, if it exists in reality, it is realistic
If proof requires certainty, then arguably nothing can ever be proven
Every day that you wait, you get closer to the release of CS3. I expect that Adobe is spending a great deal of time to make CS3 utilize every core it has at its disposal. The recent 10.4.8 update saw significant improvements in Rosetta.
Mac Pro - Octo - 2.26 GHz - 12GB RAM
Macbook Pro 2.0 GHz 100GB HD@7200RPM 2GB RAM
iPhone G 32GB
I have a G5 quad and it's fantastic. It doesn't theoretically scream, it actually does scream. No Rosetta. If you're a professional user or serious amateur [using the Adobe Suite], then the G5 Quad is the only machine for you. To be honest, I have no idea why people who use CS2 and a myriad of other creative-type, design software packages [e.g. 3D, CAD] have been so keen on upgrading to Intel boxes. The G5 quad runs circles around the intel quads in Photoshop ... so why upgrade? Future software will be Universal and Apple has promised to support PPC for many years to come so don't fret. Who knows when CS3 [universal] will come out or any other slew of high-end design apps. Computers are not investments, they're tools. G5 quads are fast, stable and hey they're liquid cooled - how cool is that? The only downside is that you can only toss two HDs in the case - that sucks.
I think you have to seriously consider what you have right now in respects to software, because that is the real question.
The performance hit of Rosetta varies, but I can guarantee you that the Adobe products run much much slower on the Intel machines than even some older PowerPC Macs.
If you have the means to purchase a Windows XP license, and have Windows version of Adobe suite, or have the money to purchase it, then the Mac Pro will likely work for you in its full glory right away under Boot Camp, but if you are in serious need of performance from Adobe software now, get the Quad.
It is about your needs and your current software.
Actually, MacWorld has a great Article series running right now about the G5s vs. the Intel MacPros. They're saying that with 2GB+ of RAM, the MacPro will run around all but the highest-end G5s even with Rosetta.
At work I use a 2.66GHz MacPro with 2 gigs of RAM. Photoshop is fast, no spinning beachballs. Its impossible to tell that its being run under rosetta, and when Adobe realeases the UB of Photoshop you can expect speed increases.
If you are gonna be working in FinalCut, then being able to put in 3 more HDs will be a boon.
The reason I'm was leaning toward the G5 is that I can't stand the idea of runing PS & other APPZ on "Roseta" and possibly seeing that dam beachball.
The only thing that runs PS faster than a Mac Pro is a Quad G5, and that's until Adobe gets the Universal PS out. That's according to most reports I've read. Rosetta is actually quite fast and received a speed boost in 10.4.8.