It's been bomb proof here for quite a while after sorting out the X2a upgrade debacle.
 
Upgraded to Windows 8 recently and it's still very stable if not more so. 
 
I did a lot of research before deciding on what motherboard etc.

aixmusique
Who works with Sonar X2 Producer without crashes and dropouts on PC?

Not me.

Works great for me. See my sig for system.  No Internet connected, virus package disabled.  ALL automatic updates off...
 
Best,
Rob

I do not recall a crash with X2a Producer at all.  I don't run synth heavy (typically 1-3 per project), mostly audio.  I use lots of take lanes, and use ProChannel heavily.  I use V-Vocal freely, and although I've had some glitchiness with V-Vocal NO crashes.  I use 64 bit plugins where possible, although not all.  It's been very stable for me, couldn't be happier.

MorganT
I do not recall a crash with X2a Producer at all.  I don't run synth heavy (typically 1-3 per project), mostly audio.  I use lots of take lanes, and use ProChannel heavily.  I use V-Vocal freely, and although I've had some glitchiness with V-Vocal NO crashes.  I use 64 bit plugins where possible, although not all.  It's been very stable for me, couldn't be happier.

I'm with you, Morgan T.
 
I do find it odd with these threads that many people respond with positive and negative experiences, and yet so many people end up saying that all the negative responses have put them off upgrading.  X2a has been rock solid here.  There are improvements that I would like to see, but no crashes.
 
Depending on the project: many audio tracks and many MIDI tracks, ProChannel on each one, and VVocal only sparingly, and only one crash since the X2a update.
 
Running well here.

I crash the silly thing all the time, well a lot. It usually happens when looping and trying to find sounds, the shorter the loop the more likely it's going to crash. I tend to have pretty high track counts for most of my work, 50-100 is pretty normal. I use my UAD card a lot (32 bit plugins) but I don't think the crashes are related.
I've gotten used to hitting ctrl-s whenever I change anything, at least I don't loose 1/2 hours work anymore.
 

ta7
I had loud audio clicks at the first time. Now i'd disabled "use Multi processing engine" in audio settings and now it works very fine without clicks.
 
Cheers, Tomas

If that solves pops/clicks, that's good...
But disabling multi-core processing will severely decrease performance
 
 

Hi Guys! Thanks a lot for every comment! Very useful to me indeed! I'm just thinking to that point: the majority of you work with Intel's processors and have no troubles; I have an AMD Phenom x4 and have crashes with my Roland quadcapture: my configuration: AMD Phenom 945 16Go ram 3 HDD (250, and 2 1000 gigas) gigabyte motherboard with amd chipset, Roland Quadcapture. I use quite a bit of softsynths: Kontakt, Omnisphere, Waves plugs etc..

aixmusique
Hi Guys! Thanks a lot for every comment! Very useful to me indeed! I'm just thinking to that point: the majority of you work with Intel's processors and have no troubles; I have an AMD Phenom x4 and have crashes with my Roland quadcapture: my configuration: AMD Phenom 945 16Go ram 3 HDD (250, and 2 1000 gigas) gigabyte motherboard with amd chipset, Roland Quadcapture. I use quite a bit of softsynths: Kontakt, Omnisphere, Waves plugs etc..

While I am currently running an Intel-based PC, my go-to gigging computer ran a quad-core AMD, and never gave me trouble with crashes.  
 
Bob Bone