I also think that a fast I/O subsystem is more worth than 8 or more core cpus.
At the moment most software is still not there. Take a look at Mr. Chambers tests (or any other site doing benchmarks on Photoshop). PS and LR have still a lot place for improving performance on many core machines. They don't scale well. And I estimate that it'll still take some iterations of both programmes before the can efficiently use every core in 8 or more core machines. This isn't only PS's and LR's problem. The vast majority of software is not optimized for high degrees of cpu parallelization. And the major desktops oses (MacOS and Windows) are only now beginning to improve in this respect. Vista/7 and MacOS 10.6 are a big step forward in that regard but both have still plenty of room left. So, hardware at the moment is quite some way ahead and software is only beginning to catch up (3D seems to be on the fore in this regard).
So, a high clocked 4 core system is in most cases as fast (or at least not that much behind) as an equally clocked 8 core system. Yes, of course, depending on how many programmes are running in parallel, responsiveness will likely be better, but the individual programmes will most likely not execute (much) faster.
So, fast SSDs (maybe in RAID 0 or similar configurations), a high clocked (i7) cpu, as much RAM as one needs to fit the largest files in (plus some), is the current way to go for a photographer's workstation in my opinion.
A server for centralized storage of documents and other data is also a good idea when one syncs between the workstation and, say, one's laptop. So even if (or rather when) the workstation is under full load one can still get all the other work done.
Ah, and the advice of getting a card with much vram is especially true with MacOS based machine but also with Windows based ones since both systems try to keep the graphics on the card. For MacOS see: AnandTech
and Ars Technica
with the later going quite deep into the matter. In the AnandTech article you can scroll down to the end where he gives an example of memory usage in PS CS4. I haven't found anything similar for Windows 7 but this: Ars Technica
. Still, more vram helps