Open Workgroup Manager and select the appropriate user group.
Next go to Preferences and then click Details.
Select your Safari preferences (com.apple.Safari). Next select/open Often (Always should work as well).
Click the disclosure triangle and then click New Key.
Click on the new key name and choose edit from the list which appears.
Type WebIconDatabaseEnabled as the Name, change Type to boolean, and leave the Value as false.
Users of the group you just changed will no longer have Safari 5 crash when they login next (at least for this particular issue). Other than losing Favicons.