Just generalized instability and "weirdness" for lack of a better term. The problems always seem to go away after a fresh load.

It sucks that this is required, but between Time Machine bringing my apps and settings back, and launching the upgrade at night before bed, it's not really that much of an annoyance.

I'd still rather use OSX than any other OS at this point. But I think we need a Snow Leopard 2, a release that only tightens up the backend stuff with no new shiny features.