Cache smearing seems like it would suffer from the obvious problem of invalidation. The solution they come up with is rather than having a piece of data associated with one cache key "foo" it is associated with "foo0, foo1, foo.., foo8".
If you have one key you can just delete it, but now you have to do that on all the possible versions of the key.
(Of course if they're relying upon TTL settings for expiration then this doesn't matter.)
