Got my Quadro 4000 for Mac installed now.
Card is rather loud at startup, but throttles back about a minute or two after bootup. It is still louder than the near-silent GT120 after throttle-back, but very tolerable for how much power it uses. It does run scaldingly hot, though, compared to the GT120 (touch test).
On the Windows side, wonderful card, but it won't play along with a GT120 simultaneously installed in the system (works fine under MAC OS with both, though) Given that I got the card for running Solidworks under Windows 7, I rather appreciate that this part of things works well.
On the mac side, it could still use some work. While quite a bit faster than the GT120, the current drivers don't have OpenCL support (useful in Capture One 6). Likewise, as per OpenGL Extensions viewer, only upto OpenGL 2.1 is fully supported under MacOS, but this is likely Apple's fault.
I also found that with the Quadro 4000 installed (using the drivers from Nvidia's site for 10.6.5), Starcraft II will no longer launch. It loads fine, and hangs at the battle.net login screen. I can still move the mouse around and sound continues to play, but I can't click and/or type anything. Only way out of it is to reboot system.
I got in touch with Blizzard to see if they can replicate the issue and/or get NVidia to look into it.
I don't yet use any CUDA applications so nothing to report yet on that front.
Will keep ya'll updated as to anything further.