How can you efficiently determine if any of the items in a List don't inherit their security from the List?
You could use SPListItem.HasUniqueRoleAssignments but this would require iterating through all items in the List.
Leading on from @tylerrrr07's answer, there's another overload of
GetItemsWithUniquePermissions which may be of use to you:
You could then avoid the potentially huge result set from running the method by using the following:
SPList.GetItemsWithUniquePermissions(1, false).Count == 1
Haven't tested it myselt but it looks like you could do something along the lines of
SPList.GetItemsWithUniquePermissions().Count > 0;