The word hopefully is an adverb; notice the -ly, which to an adverb is analogous to the stripes on a zebra–most adverbs have them. An adverb is a word that describes a verb, so hopefully is a word that describes how something is done. Charlie Brown skipped hopefully down the street means that Charlie Brown skipped in a hopeful manner down the street; it describes the way in which he skipped. It’s an active process; in other words, it’s something that we can control.
The adverb hopefully, then, should not be used synonymously with the phrase I hope since hope, in this instance, means a wish or a desire. When we hope, the outcome is out of our control. In other words, it’s a very passive act, and using hopefully for I hope is a grammar error.
I’m not saying that there is anything wrong with hoping, of course; however, we always have more success when we actively pursue things than we do when we wish for the best. So, my adivce is to be active–decide to use these words correctly.
–Paul
Paul’s book–Literally, the Best Language Book Ever
Everything Language and Grammar 