It's definitely related to snow leopard. There is always a risk of problems in major upgrades like this, and while I didn't have problems where I feared I would (3rd party wifi USB adapter due to airport card problems), I've run into them elsewhere (Photoshop CS).
I had a spontaneous segfault yesterday at work. The kind that darkens the screen and gives the message. It's the first I've had since the SL upgrade. I thought the spontaneous logout was a segfault (the log messages seemed to indicate such) and it was just better at recovering from it. I've gone through all my library folders and weeded out old software bits as best I can. I do have a MS corded keyboard and bluetooth mouse that I use at work with the drivers. If that's the cause, it was a week and a half before it showed up. I think I was just saving a file in BBEdit when it happened... I'm primarily a programmer. I use open office, not MS office. I've been able to use Photoshop for short periods, quitting the application after and reloading it if needed. But I always fear that I'll lose my work so don't spend the time on it that I would have. Adobe reports a potential crash when saving files from any of their products so saving often isn't necessarily a good way to avoid problems.
While restarts are ok, I have trouble logging out of one account and getting the login window back. I use a file vault account at work and logout at the end of the day. For the first few days, I just got the light blue background or the desktop photo but no login window. The machine would sleep just fine and wakeup to that state. I found in syslog that it was reporting a problem writing to a crashlog so I deleted the old logs and that improved the problem. Now it just takes several minutes to come up... several minutes past the usual "recovering disk space" etc... I don't have a backup drive at work so it's not that. I backup at home since it won't backup filevault accounts while logged into them (always been a problem.)
I don't know... in some ways, SL is better. But when I installed 10.5.8, my laptop had been up without a restart for 47 days in a row which is the kind of stability I've come to expect. Lately, I've been restarting as much as I was with the Dell laptop work gave me to use.
Michael