I've quickly scanned through some of the content. There are all kinds of books there. There are some self-published books, classics, and also in-print computer manuals. Needless to say, some of these works are protected by copyright law and unsanctioned publishing is certainly in violation of the law.
However, I would think that the website would probably approach copyright violations the same way that YouTube did. It will probably respond well to takedown notices. However, it cannot really control the content that it's users choose to upload.
Just like YouTube, it uses Flash technology to deliver books to the user, which is kind of cool. Unlike YouTube, it allows users to download the books in a variety of formats, including PDF and Word documents. It also has an option for audio book format but I did not try this out.
Knowing that both Google and Microsoft are going into the book search business, this website might actually be banking on that. It probably hopes to be as successful as YouTube and be bought out by one of the big companies. Google bought out YouTube for USD 1.6 billion even when Google Video was already flourishing.
So, if you have not yet heard about it, maybe it is worth a short visit to see if it is any useful. If it's collection grows as fast as YouTube's did, then it will have a huge amount of books in no time. Where is all this YouTube madness going to end?