If you find yourself saying 'honestly' often, you're probably lying too much.
As in, "Hey, Bill, what did you think of that CD I lent you?" "Well, Frank, honestly, I didn't like it very much." In this and in many cases, 'honestly' is being used as a euphemism for 'you're not going like what I'm going to say, but here it comes anyway.'
But it also is an unconcious admission that you lie a lot. For many, it's a euphemism for 'I'm a bit deceptive with a lot of the things I say, but for a change of pace, here comes a bit of honesty.'
Yep, that's Honest Abe.