Yesterday I was testing different drum libraries and instruments. So I had more than 10 soft synths loaded, some of them, SampleTank 3 SE e.g.,  with more than a single drum library. Although I have a nice Focusrite soundcard, I don't bother turning it on when testing things, so Sonar was set with WASAPI driver running built-in sound card at 12ms latency setting. Took me quite a while, i.e. several hours, to trigger different VSTis, load different libraries, switch MIDI channels, tweak MIDI data, etc.
Drum libraries are large, so the testing project required 11 GB, and I had a web browser open with lots of tabs (apx. 1GB memory footprint). Well, I had NO performance problems whatsoever! And my PC isn't powerful, it's a Core2 Duo based machine with only 8GB memory. I'm impressed, really impressed with Sonar stability and performance.
Running out of memory on a outdated PC with just a built-in audio set to a very low latency while having more then 20 web pages open in a web-browser... Oh my, that's impressive! I'm proud to be a Sonar user and a member of Cakewalk community.
Lots of thanks and respect to Cakewalk team!

Mine rocks too.. Every update makes it a little better, give or take a minor quirk.

Wish I could say the same... I think it's locked up on me about 7 times in the last week. Not sure if it's related to the new update or the new project I started since that update, but there a lot of infinite loop bugs or similar, it seems.

Mine has been very stable for quite some time now. Happy camper here  

Have to say that the Platinum releases have been very stable for me. Mighty prestige effort on Cakewalk's behalf to get this sort of consistency month after month.

I'm running an arguably older mobo\cpu\ram configuration and I have been very pleasantly surprised.  So far, I have only had one occurrence of something odd, and that happened a version ago.  The startup screen didn't draw the projects - just sat there.  It hasn't happened since, and it was NOT a problem for me.  Since startup speed has greatly increased for programs and OS since installing 10, all I did was just close and restart.    
 
Mission critical project work has NEVER failed since Platinum was loaded on this box - not once.  I am on it 5 days a week, at least 4 hours a day. Thats about 250 days or so - about 1000 hours.  To be fair - I only run three products - Platinum, AVI Motu drivers, and Waves.  I also do not do a lot of MIDI.  20 to 30 tracks of audio, 8 to 10 submix busses, 44.1 24 bit, and maybe a midi drum track until I get actual drums recorded.  I also use effects sparingly - and try to get the sound right - before I record, if I can - thats arguable certainly.  I master after the fact. 
 
Best Regards

Sonar is quite stable but it depends heavily on good external component configuration to operate reliably. If I'm  having lockups and freezes after an update, my first action is always to reboot to insure no holds on dll's, uninstall my interface drivers and the reinstall them, the reboot again. This nearly always resolves my issues. Good lick!

I wouldn't say 'definitely'. I've had plt stop working when clicking on the start screen to search existing projects...on several occasions. I've also experienced issues with boost 11 on the master bus and projects either crashing or refusing to open until removed. The latest Jamaican updates has caused timing issues on several of my soft synths including beta and there's a scanning of vst's issue as well, so I'm on Ipswich unable to update...and of course tech support still hasn't responded after 4 days.  
 
So for whatever reasons, not as stable as it has been. 

Big time stability here even on an older machine..

Sonar X3 is a great program but I always felt on my 32 bit system I was juggling effects and synths so as to not max out the 3GB of usable memory installed. Since the 1st or 2nd update of Platinum however, I can load those extra few effects or extra synth or two before maxing out. Very pleased with the stability too, haven't had a lock up or a crash few a few months or so. May have something to do with the fact that I'm trying to pare down my use of effects, but all the same, it seems stability is good these days, can't wait till I do the upgrade to 64 bit.