Just out of curiosity, are you guys at liberty to discuss what was causing the Nvidia/Mac Book Pro flickering issue?
To be honest, we weren't sure what changed in the Nvidia driver in 10.6, as there wasn't much in the way of a change log for it. After 10.6.2 came and went without a resolution in the driver, we began systematically running through how events were received, refreshes were processed and windows and GL contexts were created; a fairly lengthy process for an app the size of Houdini. Because the flickering issue was sporadic instead of constant, my guess was that events were somehow pouring into Houdini differently.
After confirming this wasn't the case, we moved onto looking at the window/context setup. We ran through a variety of changes to the setup until one particular one stopped the flickering (the BackingStore attribute). I'm not sure how this fixes the issue, or if it just happens to be a workaround, as the backing store is normally reserved for optimizing refreshes for helptips and menus (especially since the ATI driver works just fine without it, and so did Nvidia, pre-10.6). All our windows are double-buffered, so things should work just fine without it. We logged this information with the original issue report we sent to Apple, in case this helps shed some light on a potential issue in the driver.
I apologize for the length of time it took to resolve the issue.
The reason I'm asking is because Macs are pretty stable in terms of architecture, however, I was pretty disappointed that when configuring my custom late 2009 machine to pretty much run Houdini, there were no options to choose a better graphics card, and albeit from a different manufacturer, i.e ATI.
The choice to only include the Nvidia GT120, with a mere 32 shaders, did seem a bit strange. Perhaps for high-end work, they simply recommend the 4870 as a better option to what Nvidia had at the time (power requirements? or perhaps it was political..?). At least now there are a couple of third party options for Nvidia cards (EVGA 285 Mac Ed, PNY QuadroFX 4800), but since you can't buy a Mac without a graphics card, I'm not sure what you'll do with the GT120. Perhaps with the release of the Fermi Nvidia cards, the choices will change yet again in favour of Nvidia. On the other hand, the ATI cards have been rock solid on the Mac, so perhaps there's no rush.