A sad, sad sham of a word intended as "to an excessive degree." Ironically, rather than simplifying things for those with short attention spans, the use of "overly" adds syllables not to be found where the prefix over- (as in overly confident/overconfident) or the adverb "too" (as in overly tired/too tired) are employed. Seriously, are these people incapable of "too"? What about "excessively" if you want to sound smart? Overly retarded, that's what it is.
If I hear one more person say "overly" I'm going to get overly angry and cave their face in with a shovel, then dig out their brains with a trowel and feed the goo to some vegetarians who say "overly" a lot.