The video card debate raging onward.....
My 1st. gen. Mac Pro with X1900XT video hasn't ever really "crapped out under heavy load". I think *once*, I managed to get it to overheat enough to start drawing random "garbage" pixels across my screen. After that, I installed one of those 3rd. party fan control applications, and configured it to turn up the default "slowest" speed of many of the Mac Pro cooling fans to a little bit higher speed. Now, overall temps. in the case are lower - and I haven't had the video issue again either.
Other people (see notes on
www.xlr8yourmac.com) have had success putting better cooling fans on their X1900XT cards too. Granted, this solution costs you a little time and money, but it's a viable "fix" if it's giving you a lot of grief.
I don't see why I wouldn't recommend a new Mac Pro to someone interested in that type of system. The big "news" with it is, you're getting a whole new motherboard chipset and faster bus speed, and it takes correspondingly faster RAM. It's not like they're just selling you a "warmed over" 1st. gen. Mac Pro with better CPUs plopped onto it.
The video card "issue" is interesting to watch people fume over, because until Apple announced they even had an 8800GT option at all, people seemed mostly satisfied with their X1900XT cards. I sure never saw all the screaming about their multi-thousand dollar Mac Pro being "junk" and "obsolete", at least.... Rather, most people concluded that the biggest limitations to performance still lay with software that wasn't optimized to really use multiple processor cores/threads. The main reason people forked over the bucks for these "Pro" towers was often to reduce rendering times, and that's a CPU issue.... not a video card issue.
From everything I'm reading so far, it sounds like the 8800GT doesn't work in older Mac Pros simply because its BIOS is only EFI64 compliant, not EFI32 compliant. (The ATI X2600HD card, by comparison, has both EFI32 and EFI64 support in its BIOS chip.) This could very well be because the 8800GT has a lot more code in its BIOS and both versions simply didn't FIT in the thing at one time. That being the case, Apple would have to have nVidia build a seperate EFI32-only BIOS version of the same card to sell you for older Mac Pros. Maybe they'll do this? But surely, they wouldn't do this right now - when the card is in short supply and needs to first and foremost go in brand new systems for people.
Apple doesn't want to cannibalize new system sales on delayed orders for existing Mac Pro owners. I really can't blame them for that. I'm bummed too since my 1900XT craps out under heavy load because of heat. They never really fixed that problem either.
There's a pattern I've seen when Apple releases new hardware. Those who buy within the first 90 days get screwed. They drop prices in the case of the iPhone and the 1900XT once the hysteria goes away.
The only thing we can do like timb said is wait until 1) 10.5.2 is released and the 8800GT drivers are available and 2) the demand for the 8800GT's drop off. When that happens, someone will hack a ROM for PC cards like the 1900XT or Apple will fix the problem. It takes Apple a long time to realize they've got a full blown scale revolt on their hands.
I would suggest not recommending the new MacPros to anyone. If they're willing to snub Blizzard and their 80+ 2006 MacPro's, too many Apple employees have been sucked into the irrational reality distortion field.