I just read a post over at JDGreear.com where J.D talks about Piper's views on preaching.
It's great stuff and well worth reading. Piper makes some challenging statements which you should read in the context of his article. Things like "Preaching isn't Church but serves the Church", and that he, Piper preaches 40 minutes, not aiming to be immediately practical but eternally helpful; and in preaching, he is not relaxed!
Oh for more expository preaching! Real food for the living.