What was your FirstClass server / where was it? Mine was used by a large-ish (2.5k people at peak) Macintosh User Group in Canada.
It was definitely formative - I still have friends from back then, and remember logging on daily.
As you say, the transition to the real Internet and web was painful/slow for them, and obviously being a commercial software made it especially hard. The software and the user group all disappeared around the same time - hard to say which came first.