OS X is more stable than OS 9 in some ways, and less in others. OS X reminds me of Win NT (which is loosely based on VMS). When I was an NT admin, I had some NT systems that never crashed--I mean never. Apps would occasionally die, but I never saw BSOD. I had other systems that crashed repeatedly and kept requiring clean installs of the OS.
OS 9 crashed a lot--fact of life. But I found that the crashes were unpredictable and not likely to recur in the same fashion. I've had four different Macs running OS X and found that a crash will keep occurring if the cause of it isn't fixed. OS X is picky, picky, picky about hardware and software configuration.
We had an iMac 333 that ran OS 9 for a couple years with the usual amount of crashing. We couldn't install X on it without a fatal crash. A Mac repair shop finally did install X, but only by replacing the iMac's processor card! It was defective all along, but who knew?
We have a PB 867 that came with X installed. It was stable. Until we installed the QT 6.01 update. It made almost every Apple app crash. We had to do a clean install, fix permissions, remove preferences, etc, etc, I can't remember all of it! There always seems to be some app that isn't working on this computer.
On the other hand, our iMac 500 runs OS X without a hitch and always has. The same QT update caused no problems.
OS X apps are, unfortuneately, more like Windows apps. They are modular and install pieces of themselves in various places. Safari broke your IE install, probably because it replaced some libraries that IE uses. And yet, Safari didn't break most users' IE just like QT only caused problems for some users.
I don't pretend to understand it. We've called Apple--if they understand it, those people aren't answering the phones.
BTW, have you tried using a different keyboard? Another Apple KB? A 3rd party KB?