My Mac Pro is sad. I get random storms of applications crashing with illegal instructions, or memory access violations. All the kinds of things that are symptomatic of bad RAM. However, taking out either half of my memory doesn't help, and extensive memtest testing reveals no problems.
At this point, I strongly suspect a flaky power supply or some other motherboard or daughterboard issues.
I was on the phone to Apple to try to set up a repair. It's very bizarre, but you can't really have them send somebody out to fix your Mac. I've been bitching for a while about how terrible Dell computers are, but at least they'll send somebody to your office to fix the problems right away. With Apple, you have to physically bring the machine to an Apple retail store, and have a "genius" at the genius bar look at it.
Setting up the appointment was fairly easy. But I am not looking forward to dragging a 35 pound machine to the Mall the week before Christmas. Don't these people serve a lot of corporate/professional users? Ugh.
I'll post here with my experience. Maybe it will be a good one.
Update: Sitting at the genius bar in the Apple store at the mall the week before Christmas was not the worst consumer experience I've ever had. While my genius was trying to get some diagnostics running (and generally failing), about every 15 seconds somebody came up with a broken iPod. I now can recite Apple's iPod replacement policies by heart. (The short version: stuff breaks and gets old. Get a new one.)
I ended up having to leave my precious, precious workstation at the Apple store over night. Someday, I hope that we are reunited. I miss you already, buffy, and this G5 I am using now to type this post means nothing to me. Nothing.
Update 2: The geniuses called me and said everything was fixed. Apparently, I had the RAM installed wrong: there are two daughterboards for the RAM, and you need to split it between the boards vs. filling up one then the other. I asked why the machine worked fine for 4 months prior to this week, if the memory was installed wrong? They had no answer. I was skeptical.
I drove to the mall, picked up the machine, and brought it back to the office. 2 hours later, it's crashing again, same problem. It's not fixed. I am now reinstalling the operating system from scratch on a brand new hard disk. I think it's a motherboard or power supply problem, but I know Apple will ask me to reinstall the OS. So I'm doing that. Then I'm going to call them and ask them to send me a replacement unit.
Update 3: I reinstalled the OS. I decided to install it onto a striped RAID set, so improve performance, and because I only had 160GB available. (I didn't want to use the old drive at all, so I can restore my files from it, and in case it is somehow malfunctioning and the cause of the whole problem.) Everything went smoothly, the machine booted up fine. After I installed the latest patches from Apple, however, the machine would kernel panic on every boot. I called Apple and they suggested a reset the PRAM (option-command-p-r keys during power on until you hear two chimes). The machine then started to boot, panicked again, but then reset itself and booted OK. I'm continuing the process now of restoring the machine to working condition with my files and tools.
Update 4: I finished restoring all software tools and applications on the new drive set. I've been running now for 24 hours without a crash. I'm now hoping it was a bad disk somehow, that would mess up on page faults or something. Keeping fingers crossed...