Finder/Quicklook/Preview/Safari plug-in crashes noting sandboxd errors

I can do a clean install, and Mountain Lion works great then.

However, once I migrate my old Lion setup into it, it's a disaster. Finder crashes in cover flow view. Same for icon view. No icons shown to the right in Finder column view. Quicklook crashes. Preview crashes. Safari plug-ins, like Adobe Flash, crash.

I removed all my Quicklook and Quicktime plugins. Still crashes left and right.

Clearly, something is conflicting somewhere. I have no idea what. The log is full of sandboxd errors showing processes trying to read files that they don't have access to right before most of the crashes.

I guess I may have to live with the clean install? What a PITA.

Anyone have anything like this?