I've had Knockout 2 for many years and always found it too fussy and tedious to use, and not worth the time and effort compared with the results. The improvements in masking programs, from the tools in CS5 and Topaz Remask knock Knockout 2 out in one round!
While it is a shame that computers go obsolete so fast, the advances in Photoshop, NIK Software, Topaz Labs and much of the HDR software make processing my images so much easier, better, faster and more reliable than even using the CS2 and compatible software.
I do not have a MAC, but a PC because the same processing horsepower is much more expensive with a MAC. I have chosen to use my meager piggybank for software updates and better camera/lens equipment rather than whatever advantages a MAC is supposed to have over a PC.
I believe that if I had MAC that is no longer supported I would be very tempted to get a really powerful PC for around $1000, buy extra RAM for it, and take advantage of the great advances in software.