I'm happy with X2 - no crashes yet. I'm a big fan of X1 and it would only occasionally crash on me - I expect a few crashes here and there with X2 as well. Time will tell. I've never heard of a crash free daw program.
I did have a head scratching quick groups moment. But that aside, I don't see me opening X1 again to do my work. Really liking X2. The audio engine is great, and the tools are great as well. I think X2 may be the daw other developers start chasing now.
On Vista64 here too John. I don't see a big need to change at the moment.