Hasn’t been my experience. There have been some buggy unstable releases of MacOS, to be sure: 7.0, 7.1, 7.5, 8.0, 9.2…but 9.0.4 is a log way from “absolutely horrid” stability-wise. It’s better than Windows95 / Windows98 / WindowsME, in fact.
I’m still waiting for OS X to catch up. Oh, sure, the OS is solid as a rock and never crashes, but the individual apps do, and frankly I don’t much care if it’s FileMaker or the operating system that died on me if my environment goes down while I’m in the middle of doing field definitions. All in all, my ancient 7100 running 8.6 is a more trustworthy environment than 10.2 on a G4 tower and so I Timbuktu into the 7100 to do my field defs.
I’m upgrading nevertheless as soon as there’s a dual-processor G5 PowerBook to upgrade to. With that much crunching power I can run MacOS 8 in a Basilisk window at decent speed if I have to.