I really think that there is ABSOLUTELY no reason to ask money for a PDF of your entries or selling your book (if you see what I mean). It should be provided to everyone. People who can donate give some money and help to bring the service to people who can't afford it or don't earn money yet.
LJBook converts your entries into another medium (and I hope you agree: nicely). So you get YOUR LJBook, with YOUR entries, and you do whatever YOU WANT with it (publish, sell, give, ...).
You hold the rights, it's YOURS! (but bandwidth is not yet free...)

Already more than 900 livejournal's users donated to this project. It's thanks to them if the FREE service can be provided.
Some are listed on the donors page.