X1d was very stable for me but X2 not so much just yet. On my laptop (old AMD Turion based HP), I can't even launch X2 without it crashing my machine hard every time. The only way it will come up is if I have my Saffire Pro 14 turned off. X2 doesn't seem to like it. On the same machine, however, X1d has been running with same interface/driver combo without issue. I've reinstalled X2 a couple of times over the weekend and no luck.
On my desktop (custom built core i7 930), no BSODs, just the SONAR white out after performing some basic operations, e.g. dragging an FX chain into the Master Bus PC, bouncing 5 softsynths to an audio track, and a couple of others. I haven't been able to spot a trend at this point...
I am hopeful, however. I really like the new features, additions, and audio engine improvements as they are all positive polishing and refining. I think Cakewalk's execution is sometimes too obviously flawed but I am convinced they really care about their products and customers and that is a high value for me. The Bakers have done an amazing amount of work and improvement over the last ~24 months and I think they are heading in the right direction.
Now, if that crashing thing can just go away again.............