[Haskell-cafe] deepSeq vs. rnf?

Now and again I see references to "deepSeq", and I've never understood how this could be any different than using rnf from Control.Parallel.Strategies. Is there really any difference? When is it better to use one or the other? Thanks, -- Chad Scherrer "Time flies like an arrow; fruit flies like a banana" -- Groucho Marx