Bodacious is an Americanism that has been around since at least 1837. It originated in the South, and was used to mean 'bold'. It may be a portmanteau of the words 'bold' and 'audacious'; it might also be from 'bodyaciously', meaning 'fully, throwing one's whole body into it'.
It currently has come to mean not only 'bold' but also 'remarkable', 'wonderful, 'audacious', and 'spirited'. It generally has positive connotations, unless the context indicates otherwise.
It was re-popularized by the film An Officer and a Gentleman in 1982, perhaps resulting in its more recent popularity in surfer slang, where it is used as a synonym for 'cool' and as an all-around intensifier.