Other user accounts on the same machines worked, just not the main upgraded accounts. Rebooting did not help.
The solution for me was to Control+Click on the Finder Icon and Relauch it.
[crarko adds: This sounds a lot like corruption of the user's Finder preferences (~/Library/Preferences/com.apple.finder.plist) or cache (~/Library/Caches/com.apple.finder). If you have this problem and the simple fix of the hint doesn't solve it you may want to move these to the Trash, logout/login and let Finder create a fresh set. At times in the past, iCal windows were also susceptible to this problem and trashing the iCal prefs and caches was the fix.
Changed Option-click back to Control-click. My fault.]

