Not sure if this will help most out there or not, but here is my own crash story.
I first installed FPCX onto my laptop, a fairly new thunderbolt MacBook with no problems at all. You see, I was working on project in FCP7 on my main Mac Pro and didn't want anything to happen while in the middle of that project. However, when I was finished and backed up with that project, I decided to install it on the Mac pro as well.
In both cases I installed it alongside FCP7 on the same partition. I understand it's not recommended but I followed the "best practices" FAQ from Apple. But where I had a stable installation on my laptop, my desktop installation was very buggy. Specifically, adding the placeholder generator or the artifact effect to a timeline would result in a blue screen and eventual crash.
After many reinstalls, and deletions of preferences, I deduced that there was something on my desktop that wasn't on my laptop and whatever that was (program or library file or something else entirely) causing the instability.
Thus began my three day project of completely wiping my main hd and reinstalling all my programs and preferences. It wasnt an easy task, and required a lot of planning, but it was the only way I could see if there was a particular culprit behind the FCP X instability.
Now, before I had installed FCP X on my desktop, I had backed up my main drive to another drive, so I knew if this didnt work, I'd still have my old system available to go back to.
One thing I did different, was I installed Snow Leopard from the start even though the original OS for my desktop was Leopard. My laptop had always been a SL machine, so I figured I'd make my desktop one as well. As I reinstalled each program, I opened and tested FCP X and FCP 7, to make sure they still worked without crashing.
The good news was that FCP X became stable on my desktop machine. I reinstalled all of my programs and it remained stable, so it wasn't a particular program that was causing it to crash. Probably some junk files that accumulate on a machine that's been running for a while. Or it could have been an issue with a computer that was upgraded to snow leopard from regular leopard.
I've also not completely reinstalled all my FCP 7 plugins as I was more worried about them causing an issue than I was worried about iWork. But I've been reinstalling them a few at a time, making sure I gave a restore point to go back to, just in case. I also don't really have that many plugins, so I no longer expect any problems there.
I tenatively recommend this technique to anyone having serious crash issues. Obviously you should have a pre-FCP X backup of your drive before you attempt it. If nothing else, you'll need it to reference all the little things you need to re-set up (like smart mailboxes in Mail, FCP 7 preferences, browser bookmarks, addresses in your address book). I also recommend that if you DO try this, that you install FCP 7 BEFORE reinstalling FCP X.
Andy