The first time I read “Atlas Shrugged”, I skimmed over the 100 page radio speech.
I have since read it all, but that part was very repetitious, and interrupted both the action and character development.
In an interview that Ayn Rand did on TV (I think with Dick Cavett), she very frankly stated that the entire book was just a vehicle for expressing her Philosophy of Objectivism.
(paraphrased from a lawyer friend of mine)
Another Awful Warning is Marion Zimmer Bradley the scifi/fantasy writer. She could tell a good story if she would cut out all the feminist/lesbian/radical garbage, but seems like every 50 pages or so it's "Drop the story, let's spend 25 pages expounding my brilliant philosophy." Ugh. Only read some of her stuff because a friend was a big fan. Didn't help.
Sherri Tepper preaches too much too, but she works it into the story better (and she writes better dialogue than Bradley).