As someone who's been on OSX since Panther, I think you may have a slightly rose-tinted view of the past - lots of stuff in OSX has been improved - I remember pretty horrible kernel panics in 10.4 and userland issues in 10.5 that no longer exist since 10.6/10.7 (or have yet to show themselves). Driver support from vendors is vastly improved, and overall, though I agree that quality has been a bit hit-or-miss, the overall usability is improved, IMHO.
I've been here since 10.2 and IMO the only great releases of OS X were Panther and Snow Leopard, though Panther did begin the whole idiotic metal UI thing. Maybe 10.9 will rock?
I'm actually finding Mountain Lion much more stable than Lion or Snow Leopard. Lion had some really weird memory things and I did get multiple kernel panics in early Snow Leopard.
