OSX is window dressing for the Unix underneath - they'll just port it over.
For OS9 fans, it's the end of the road for new machines that will run the venerable 9.2 - just have to keep tweaking those G3's and G4's with aftermarket processors. (Hey, I've got a 1.4 dual G4 in a Blue and White G3 so don't laugh.)
I always thought the applications were what I used. The operating system only exists to support the applications. (And some of my favorite programs are not available for the Mac.)
It seems to me that once you are into an application on a Windows/Intel machine or a Mac/Intel machine, your experience will be pretty much the same.