Merriam-Webster's Dictionary of English Usage on awful vs awfully.
"The intensive adverb awfully was attacked as a Britishicism by Richard Grant White in 1870. The Oxford American Dictionary as recently as 1980 continues the depreciation of the intensive with the remarkable claim that "careful writers" avoid it. Perhaps so, but good writers have certainly not avoided it since it became established in the mid-19th century. Some of our examples are from fiction and drama, but others are from ordinary discursive prose"
They give 14 examples of awfully as an intensive adverb, from writers like Wilde, Kipling, James, Huxley, Maugham.