I really liked Kindle's samples in this regard. Most of it is a few pages from the introduction, and most of the time that's very representative for the those types of books. If it starts with a recollection of the author's childhood or the experiences of a client, you can ditch it most of the time…
http://www.getabstract.com/
Very nice; you can just subscribe to the business books feeds, read the 3-page PDF summaries, and decide if you care to read any deeper.