Yea I think Youtube of books is the right way to look at it, it started off as something for people to load docs up to an of course people loaded copyrighted material which was illegal but there is a lot of stuff on the site that is legal and good. A couple of the blogs I follow use it to post up docs related to articles like government or company filings because you can embed it in a site easily
I don't know how much luck a person would have just trying to search for copyrighted material on there anyway (most of the time people change the title so it can't be easily found by owners) but if you find a new book on there free something is probably fishy
They recently signed up with Simon and Shuster to provide their books on Scribd, I havent used it but here's their announcement
http://www.scribd.com/doc/16342197/S...n-and-Schuster