Most of the books on this site seem like pretty lousy books!
Many short stories, many books written by authors who would never get their books sold, and many who are just dillusional and want to show the world their weird train of thinking.
Finding a good book is like going with a needle through a hay stack.
So far I've read about 15 books of them, if after 20 pages they don't grab my attention (is what I call the grace period), or I kind of have a feeling the book won't be very good, I delete the book.
And aside from a few good tips in books no larger than 11 pages (some even with half commercial in them), I deleted all larger books.
On the other hand I've had great pleasure reading some SF books from this site:
http://www.baen.com/library/books.asp
That is Baens Free Library. Basically some writers write good books, but are not well known. They let you read their first book for free, hoping you will buy their other books.
The other books are usually a follow up on the story, meaning eventhough their first book is a story on itself, you'll need to read all the volumes to know the end.
It's a good and healthy trade, and a good and healthy way to get to know good writers!
I highly recommend the baens free library, and if possible support the authors.