I did Le Book for a few years, when it was a book(s), not a web site. Last time was 2004 or 2005. In those days it worked, but there was a shift going on, the old hands dropping out, replaced by spoiled children, or so it seemed.
The web and personal contacts worked much better for me.
One way I used Le Book was to find set builders/MUA's etc. I would seek personal recomendations and if they were also in Le Book, I figured I'd take a chance and set up a meeting. I figured, rightly, that if tehy were recomended by someone I liked, and they put up the coin to be in Le Book, they might be legit.
Ziocan's comments above are spot on, and Fred's post seems about right too.