I remember using OS
6.
[/getoffmylawn]
10.0 on an dual USB iBook wasn't stable enough to teach with, but I was playing with it from day 1 to evaluate it for design and lab use.
I might still have classic on my old G4 mini (to play Alpha Centauri or to load archaic backups), but effectively migrated to OS X well before 10.2 was out.