Steve Jobs seems to think that adoption of OS X is pretty slow:
At the start of the year, Apple had only 1 million of its 25 million Mac owners actively using OS X. That number is now in the range of 1.5 million to 2 million, although about 3 million Macs have been sold with the new OS on the hard drive.That 5 million figure must incorporate an expansion of their market; even with that large user base, it would represent at best 20% of the Macintosh market, 16% at worst (if every OS X user is a new Mac user).However, Jobs remains confident the company can end the year with 5 million OS X users.
For all the talk about Apple becoming the largest vendor of RISC-based UNIX computers, this prognostication sounds like the OS X market is still a minority fringe.
I think the lack of support for OS 9 will kill it eventually, but it will take about 3-4 years at least for it to die completely (or reduce it to Amiga/BeOS status).