Here's another excerpt, from The Muse's Muse (full article here: http://www.musesmuse.com/columnistsgreylogs/archives/00000157.html):

"Destination Songwriting" by Mary Dawson

...we have identified the Great Idea as the essential DNA of a Hit Song and the Hook/Title as the equally essential RNA. These two indispensable elements are the core of every Hit Song and comprise its thesis or main point. Using our analogy above, the Great Idea and the Hook it is "hanging on," are the destination of our song....

....Bob Dylan's classic, "Blowin' in the Wind", is a wonderful example of the payoff Hook appearing and repeating in the refrain of an AAA Song. Each A Section or verse of the song begins with a series of questions which are a very effective way of "setting up" the Hook to really deliver the answer.... Notice that the Hook appears in the same place in each A section and has the same musical and lyrical content....

As with the AAA Song, the AABA Song Form contains a series of verses with the same music but different lyrics. The only difference in this case is that the second and third verses are separated by a contrasting B or Bridge Section which adds drama and returns the listener to one more repetition of the now-familiar message and music of the final A Section. Again, the most effective placement of the Hook in this song form is in the first or last lines of each A Section. Think of the wonderful song, "Somewhere Over the Rainbow"....

Now we come to the Verse-Chorus Song – that amazing, exuberant Song Form that dominates so much of popular music in every genre. While there are many techniques for placing the Hook effectively in this Song Form, the prevailing guideline is that the Hook/Title should appear in the first and/or last line of the chorus and be the definite arrival point of each of the verses. While the verses can contain allusions to the Hook, they should not contain the Hook itself. Remember, the Hook is the payoff – the punchline of the joke....

...Most effective writers of every Song Form will begin by outlining what each verse will say and how it will conclude with the Great Idea of the Hook. As each verse adds new thoughts to the Great Idea, the Hook concludes those thoughts and burns itself into the hearts and minds of the listeners....