Beta was tough for me. I could usually only get in a few rounds before it crashed or froze. With the release version, I've logged many hours already and it's only crashed on me once (seemed to be triggered by having my city attacked by a ridiculously powerful AI army)

I had a lot of performance issues in the beta, although oddly enough not a lot of crashes.  I either had to keep it on the cloth map or not zoom way out - late game I had to go with cloth map because it was just way too slow.  Post v1.05 I haven't had much in the way of crashes.  There is some slowdown late game, however, but nothing like it was.  The one thing I have run into recently is the grayed out end turn button where it hangs between turns, which was a tad frustrating.  That has only happened on my latest game, however.

I guess I'm lucky in not experiencing crashes with the one exception of alt-tabbing.