I've had fewer lockups in OS X than in Windows. I've used Windows since 3.1 (started on DOS) since I was a little kid (3 years old maybe?) and I just recently switched to Mac mid last year. I don't have any experience with any other version of OS X but my ML install has been iffy, mainly because of bad apps.
I had to completely reinstall OS X only a few weeks after I got my MBP last year because I had installed Sophos AV, that program wreaked havoc on my poor machine. Nothing I found online would help it. Lagging, stalling, screen freezing, slow response, blah blah. I had to force restart my laptop to get it to function again (though it did poorly). But just a week ago I was having problems with my computer (mainly my web browser - any of them I tried) became slow and laggy. I uninstalled some plugins, tried rebooting multiple times, ran OnyX, make sure disk was fine, etc. I asked for help on the Apple discussion boards and someone suggested creating a new user and testing it out there. Well that fixed the issue. So I've now moved to the new user account I created. So I still have my old user sitting there in my computer. I wish I knew how to fix it.
Long story short, Windows (in my experience) is much more buggy/slow/annoying/crashy than OS X has every been in my short time using OS X. I used to have to force reboot weekly or more on any version of Windows I had. Always forcing programs to close, losing my work, etc. I've not really had that issue on OS X. The times I have had that happen, it was when I was running MS Office and it wasn't the computer that crashed it was Office. So it does seem that OS X is more stable than Windows. It just depends on the apps you are running mostly. Sophos, Office and Yahoo Messenger all crash or cause crashes a lot in my experince, in OS X. I can't put my MBP to sleep with Yahoo Messenger running because it WILL crash. No ifs ands or buts. But at least it doesn't take my whole computer down with it. So now I stick with ClamXAV even though it doesn't protect my computer like an on-access scanner would (oh well) and either I use YM or Adium or Messages whichever strikes my mood when I reboot. Usually I just deal with YM because with Adium you can't transfer files like jpg's to friends, it just doesn't work.
Long story I know but it seems on OS X that the apps are mainly at fault when something crashes, and on Windows, it's either-or. My personal opinion, ditch Windows and go Mac or Linux.
I used Linux almost exclusively since 2002 until I started college in August of last year when I had to put Windows on my machine and then that's when I decided I couldn't handle Windows anymore (which at that time was Win 7) and I used college money to buy my first Mac. I don't regret it, and from now on, I'll only ever buy a Mac.