OS9 always seemed like little improvement over OS8. The biggest thing I remember was this was when they introduced the Applications folder. It's like they were trying to get you to get used to how the structure in OS X was going to be, but with no explanation.
OS9 was really just 8.7 but, as you describe, a stepping stone towards 10, both numerically and with a few nods to the future, e.g. Keychain Access, CarbonLib, and file/printer sharing over TCP.
Carbon was a moving target; each "update" cut more core MacOS tools and added OSX service interfaces. It was quickly obvious that there was no intention of letting MacOS run in the future, so why port to Carbon? many social signals in the developer group at the same time.
Yeah, so looking back at the release dates of these, I definitely used at least back through OS 7, but I can't say I remember anything specifically about them because it's fading into the haze of youthful memories. In my mind it's all just pre-OS X and post-OS X, as that marks by far the biggest change in Mac OS functionality that I remember.
