How many people read the banner ads?
I just looked at Big Dif Books. The information was hard to find (had to jump through a bunch of weblinks first), but apparently, you can choose to sell your children's book for $1.99 per copy if they accept it.
Nothing on the website mentions fees, though I get the definite impression they'd rather you donate your book for free instead of asking to get paid for it. They offer software for you to illustrate your book and paste in your text, etc.
Has anyone checked them out for real yet? Done business with them or knows someone who has? I'm curious as to whether or not they really are legit or the "you can charge money for your book" thing is a front for them trying to get your work for free.