Adam Rosen at Low End Mac, on Mac OS 9:

What surprises me is how many people are still using a ten-year-old operating system for productive tasks. A not-insubstantial set of folks still need (or want) to run OS 9 for reasons both business and personal. We know that Macs themselves are well-built machines that stand the test of time; it appears Mac OS versions do so as well.

I respectfully disagreed three years ago. That said, I do love booting my Clamshell iBook into OS 9 every once in a while.