I've run into a couple of cases when attempting to support multiple GHC versions in my libraries (7.6.3 -> 7.10) where I've repeatedly made mistakes due to being warned about unused imports for various modules that are now part of the Prelude such as Data.Monoid, Data.Foldable, etc. which I subsequently remove either manually or via editor automation sufficiently indistinguishable from magic.
A trick is to import Prelude at the very end, like: import Control.Applicative import Data.Monoid ... import Prelude Since the unused import check is done from top to bottom, and you almost always use *something* from the Prelude, this will suppress the warning. There are some problems with qualified/explicit import lists if I recall correctly though. But it works for me most of the time. Regards, Benno