FLGB

I think that the Mac has proven it's ability to handle big projects in the 3D/VFX world. Just read the Luma Pictures story about underworld evolution.
That kind of workflow is getting more and more common everywhere as an only mac station is able to do high end video editing as well as 3D creation, compositing matchmoving, finishing, etc. It's no more needed to have a dedicated machine for each part of a work; and in a DI workflow that means more flexibility and less costs.
Ok it has some weak points like QuickTime that really sucks, but I don't think that there really are better alternatives…
Linux is in my opinion an excellent OS but is number 2 just behind Mac OS.

So concerning the port of houdini on Mac OS X; I really can't wait for that.
Maybe the change to intel processors will make the port from Linux to OSX easier. There is also the X11 alternative.
I don't think that Science-D-Visions had a lot of pain porting 3DEqualizer to mac as it's basicaly an emulation of their IRIX version through X11 and it's working quite well.
http://www.apple.com/macosx/features/x11/ [apple.com]
http://www.3dequalizer.com/ [3dequalizer.com]

If houdini goes to mac I'll be one of the first to buy it.