Deleting preferences didn't help. I switched to the Admin account to test there, and it hung with a blue screen.
What the heck was going on?
The source of this and several other bugs, including a lockup the night before, was I was performing a 7 layer erase and FAT format on an external drive being recycled for donation.
It appears than several Finder/File system related operations in 10.6 will hang when an external drive is being erased.
I've been using 10.6 for a few months on my newest machine. It's not bad, but it's still not as stable as 10.5.