From Strunk and White's Elements of Style (Commonplace Book)

Flammable. An oddity, chiefly useful in saving lives. The common word meaning "combustible" is inflammable. But some people are thrown off by the in- and think inflammable means "not combustible." For this reason, trucks carrying gasoline or explosives are now marked FLAMMABLE. Unless you are operating such a truck and hence are concerned with the safety of children and illiterates, use inflammable.

Hopefully. This once-useful adverb meaning "with hope" has been distorted and is now widely used to mean "I hope" or "it is to be hoped." Such use is not merely wrong, it is silly. To say "Hopefully I'll leave on the noon plane" is to talk nonsense. Do you mean you'll leave on the noon plane in a hopeful frame of mind? Or do you mean you hope you'll leave on the noon plane? Whichever you mean, you haven't said it clearly. Although the word in its new, free-floating capacity may be pleasurable and even useful to many, it offends the ear of many others, who do not like to see words dulled or eroded, particularly when the erosion leads to ambiguity, softness, or nonsense.