Mac OS 9 Compatibility, Upgrades, and Resources: "-
I've pretty much switched to OS X for production work, but I'm still glad to have the good, old classic Mac OS available as a standby. If you have an older Mac that is not supported by OS X - or even one of the slower G3 machines that is - there is still a strong case to me made for running OS 9, which is a great operating system. There are also certain software applications that are only supported in OS 8/9 that may be mission critical for some users."