My 10.3 has been very stable.

I've noticed that every time I upgrade with a major release (10.1 to 10.2 to 10.3), the machine performs much better on the same hardware. It's also not a small increase, but usually something like 1/2 the boot up time for example.

I guess that just means that their older releases weren't as optimized.

Also, Apple has been tweaking and honing the user interface elements every time.

What I don't like is that I have to pay $129 for each of these, unless I buy a new computer where it would be included. They have also been releasing these paid upgrades every 12 months or so. After this release, Apple claims that they will be slowing down their cycle.