"Imperial" denotes an ale which is typically much higher in alcohol, and therefore typically contains more grains, but may or may not contain more hops.
Imperial Stout probably being the most common.
Imperial India Pale Ale: Imperial IPA, IIPA, Double I PA.(if that suits you)
That's why DIPA is kinda douchey. Why use a "D" when the "I" is really the correct letter?
Epic double post.. Drinking some Stoudt's Smooth Hoperator. http://beeradvocate.com/beer/profile/394/36670 which is a hoppy doppelbock. Good stuff, with a pretty big flavor for a lager.