There is a difference on how I use my machines in the field or in the studio. In the studio I process during the shoot, I have bridge running, PS. I run actions. I adjust in Phocus. I run music, I watch television on a small window on the screen when there is something I don't want to miss. I find Phocus needs to be faster on this studio machine than it currently is under certain circumstances. I find it is slow in getting multishot images in, it slows down after about 30 shots. At that stage it gets about as fast as on my field machine, this is weird and IMO should not happen.
Besides that, I find something is too slow pretty fast. I also don't like CS4 and think it is unacceptably slow. I hope CS5 will improve in this area. Speed is also a matter of perception. Where I tend to be more forgiving when I am working on my own in the studio sipping on my excellent espresso or cappucino. I am totally unforgiving when dealing with a client looking over my shoulder and 2 female stylists which are tapping their feet on the ground waiting for a multishot image to come in.
In the field I use an early 2008 MBP 15, 2.4Ghz with 6Gb of main memory. In single shot it can cope quite easily, though (as I mentioned in an other post before) don't expect it to fly. Take the pace down a bit and use the machine for capturing and gettting the images in. I rarely process on this machine during a shoot, only if I really have to but I try to avoid that at all times. I also use this machine to do multishot shoots, with this it needs to get 4 shots in, computate the final RAW (of 228MB) and get that in. This process I find is taking too long. It works for about 30shots after which it slows down too much. The good thing is that these sessions normally are slower than the faster paced sessions with people in it.
As mentioned processing or regularly adjusting images in Phocus in the field during a shoot is not what I do a lot because I do find Phocus too sluggish for that. Things like cropping and resizing take way too long.
What I do is; I set up Phocus the way I want it, eg. filenames, storage location, WB, exposure, etc (as much as possible). I shoot, I change naming during the shoot and that is about it. Coming home, I hook up the MBP to the MacPro and pump over the .FFF files. On that machine I do post-processing.
If I really have to I could do it on the MBP but that takes longer.
Did I mention I am waiting for the Arrandale MBP's ?
BTW, the G5 is no longer, it has been Intel processors for a while now.