Ok, you can argue that CS3 runs ok on a four-processor Mac with 8GB of RAM, but I'm not talking about trying to run CS3 on a G3 iMac or something. I bought an absolute top-of the line MBP 17" in mid-2006, maxed its RAM, and put the fastest 7200RPM drive available at the time in it. CS2 was the year-old current version at the time, but was not Intel native, so ran poorly. CS3, released about 9 months later, would be the first native version available for that pro-grade Mac (portable, but still dual-core and pro-grade), and runs ok so long as it is the only thing running, period. Otherwise it slows to a crawl, even with modest-sized images.
My point isn't that Photoshop is unusable on what was a one-year-old higher-end Mac at the time of it's release--it's not, I use it frequently--just that it's ridiculously resource hungry when there's no obvious need for it to be. Really, what features were added between CS1 and CS3 to cause such a huge performance hit (other than the preposterous activation scheme)