What's the correct usage of "hopefully"?

I said, "Hopefully, I will get better" to a friend and he said that I was using it incorrectly, stating that hopefully is an adverb meaning "full of hope" that modifies a verb. It sounds right, but I'm pretty sure that this usage of hopefully has become prevalent enough to be accepted for this use case. Am I right, is he right, or are we both right?

Solution 1:

http://en.wikipedia.org/wiki/Disjunct_(linguistics) has a section about "hopefully".

In the purest sense, your friend is correct, but "hopefully" has been dated as a disjunct back to the 18th century, so I'd say it is prevalent enough to be considered correct.