Unfortunately, I'm sorry to say that my experiences were similar to the OP's. Started with Sonar 2, then 3, skipped 4 and 5 then upgraded to 6,7 and 8, ending up on 8.0.3.
Over all these versions and with multiple hardware platforms I can't say I ever had a rock-solid glitch-free experience at any time. I work in IT, so I know a bit about computers, and each platform was carefully set up to be stripped of unnecessary services, didn't run AV, wasn't network connected, and used an Edirol audio interface, directly connected to the host computer.
Either the audio engine would randomly drop out on me - especially with some plugins like RealStrat - or Sonar would crash. I learned that some Cakewalk plugs, like V-Vocal, were especially treacherous for this, but in general you could never feel entirely confident it wouldn't start behaving weirdly. I tweaked endless parameters, did DPC latency checks etc, etc but eventually one day I downloaded Reaper and tried it. I hated it at first and it lacks a lot of Sonar's depth but it never ever crashes or glitches, even with all the plugins I used with Sonar.
Now I accept that others have had rock-solid experiences with Sonar. I have no idea what magic incantations I should have made to resolve my issues - heavens above, I set up new hardware platforms, religiously updated all my plugins, and Sonar itself, and tried everything I could.
I've learned to live with Reaper's limitations - though I sure do miss a lot of Sonar's functionality. But nothing kills musical inspiration faster than a glitch or crash - it matters a lot more than if you were, say, doing spreadsheets or word processing or whatever because you're in a completely different mode of thought where the DAW needs to 'just work'.
I think - when everything is 'just so', that Sonar must indeed be rock-solid. But unlike other competing products it seems to be unusually sensitive to environmental differences and the audio engine is particularly easy to disrupt. And when that happens it just 'drops out' and that's it. And when Sonar crashes it doesn't seem to properly close the audio device driver either, so you now have to often do a complete reboot.
After I set up my latest platform, I did a torture test with the audio tracks from Sonar's 'guilty' project by importing them into Reaper and copying them multiple times. Since the new machine is a laptop with a 5400rpm drive, we ran out of disk bandwidth around the 130 track mark, but even continuing to add tracks to several hundred, Reaper gamely continued, although of course there were glitches since the hard drive simply couldn't stream audio fast enough.
Conversely you can load up effects until your CPU meter is right into the red and again, although Reaper will eventually glitch, it never becomes unstable. Sonar, on the other hand, I always felt was 'right on the limit'. If you pushed it, it just quit in various unexpected ways. Indeed (although this, to be fair, is still version 8.0.3 which is the latest I have), that version on my new platform immediately started playing up just running through the sample projects, particularly the softsynth-heavy ones like Dark European Space Adventure, which played about 1 minute and then crashed Sonar.
You can argue that I've set something up wrong on this new machine (which, BTW, has a core-i7 and 8G RAM), but it's racked up about 3 months now with Reaper and a whole pile of softsynths without so much as a glitch, let alone a crash, so I'd be very interested to know what magic pixie dust it takes to get Sonar stable on it.
And one final thing, which kinda tells me how much care and attention is being paid to quality control at Cake these days. Try going into this forum with Firefox and you'll find that preview doesn't work (a box comes up with 'undefined') and that any post will end up with no paragraphs, just a single block of text. This means I have to post using Internet Explorer. That's depressing. I know running the forum isn't the same as developing the core DAW software but I'm sure the devs must have used this forum in the past and certainly the product managers do. To complacently ignore something like browser compatibility in 2012 - nearly 2013 - indicates a general lack of attention to detail that doesn't make me confident about the company as a whole.