i thought I'd start a thread on this, since its such a juicy question.

What if you wanted to come up with the best 4-drive internal-only setup for a mac pro? for instance, a business such as a retouching studio that prefers to come up with a standard setup, and really doesn't want to have to implement external enclosures as well.
when you have multiple computers, the costs are exponential.

So, what IS the best setup for a photoshop user, when you are limiting yourelf to the 4 internal bays?

I am pursuing the following course, and will replicate it with future workstations:

6 GB RAM (at first)
4 drives internal, my preference is the Raptor 150GB

Bay 1&2 RAID0: SYS, APPS, USERS (sorry ricks)

Bay3 & 4 RAID0: SCRATCH on partition1 (first 100GB), nightly retrospect backup on partition 2 (remaining 200GB)

This setup is simple to implement, and you have some degree of backup as well. I have used and loved having the Users on a separate volume, but it takes a little setup time and I want to keep it simple. The raptor raid will be plenty fast. And if I beef the RAM up to 10-12GB I don't expect the system to do that much paging...

I'm interested in what other people are doing in workgroup environments?