For those too lazy to read the membership agreement (somewhat like I am) heres how it works:
Basically the same as Columbia House for those of you that have used that. What you get is a few books REALLY cheap now, and you agree to but 3 more over the next 2 years. Theres no way out of that one, its a legally binding contract.
The three week thing is this: every 3 weeks, you will recieve a nice package in the mail from them. In this package will be a flyer that contains all the books they have for order, and the price. There will also be an order card included with it. Now, if you do not return this order card to them with specific instructions NOT to send you the "book of the month", then they will send it to you automatically and charge you. It just becomes a hassle after a while to send it to them.
If you want this offer, what I suggest doing is pick out 7 books that you want from all of them. Order the most expensive 4 first (for $6), and then, when you get the first mailing from them, order the other 3 (or 1 book every time you get a package from them for the first 3 times). That way, you can cancel right away, and not worry about it in the future, as you've met your obligation and gotten the 3 books. You end up with 7 books, and 4 of em cost you $6 + shipping
Thats the easiest way to do it I've found. Find 3 really cheap books you think you might use, and find 4 books that you KNOW you'll use. Order the cheapest things they have after, and your set.